This play yard (link below) might do the trick. Now that we don't need it for a play pen, we've made it into an enclosure around my husband's desk in the basement. It's free-standing and since it's metal it's durable and stable. Perhaps with a 2-panel extension set and a door/gate panel (you can step over it, but it's pretty high) you can make something that will work.
https://www.amazon.com/North-States-Metal-Superyard-freestanding/dp/B000U5FOT2/
I bought a baby playpen off craigslist. The posts are vertical, i.e. not climbable. This is the amazon link. I bought 2 sets of these on craigslist for super cheap and we use the second one as a gate for a really wide hallway we have. We had ours attached to the crate with clips (no zip ties lol), until he started climbing on the crate to get out. Now his playpen is his crate during the day.
My first thought is to use something like this (https://smile.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_api_i_MXA58C14ED98S41Y759N_0) to fully enclose the bottom of the staircase and to wrap from the top of the stairs around that corner all the way along the banister.
It won’t be attractive, but it won’t permanently change the look of the stairs. How long you have to keep it up will totally depend on the personality of your child.
We have this and it's amazing. Our kid is 1.5 and it'll be a while before he can climb over it. It's metal and can be bolted to walls, or even freestanding and then collapsed as needed.
Toddleroo by North States 3 in 1 Metal Superyard: 144" long extra wide baby gate, barrier or play yard, Hardware or freestanding, 6 panels, 10 sq.ft. enclosure (30" tall, Taupe) https://smile.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_apan_glt_fabc_G4E4JTRX4YNZ9BSCXHNX
this may help Toddleroo by North States 3 in 1 Metal Superyard https://www.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_cp_api_glc_fabc_C6-6FbCZJQX9G?_encoding=UTF8&psc=1
we had a weird situation where we had nothing to mount a gate on and this did the trick nicely. you can position it so it’s very sturdy even without mounting it. however we did have it at the bottom of our stairs not the top.
How's this? The New York Times reviewed baby gates and this was one of their picks, which is why we chose it. We used it in a circle, but it should fit an 8 foot doorway. We loved it when the kiddos were a big younger. If you're looking for something even bigger to form a big circle, you can get as many extension packs as you want and hook them together.
Here’s one such gate from Amazon...
Toddleroo by North States 3 in 1 Metal Superyard: 144" long extra wide baby gate, barrier or play yard. Hardware or freestanding. 6 panels, 10 sq.ft. enclosure (30" tall, Beige) https://www.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_cp_api_i_YBVWEbE63JSHM
I have this one with 8 panels North States 3-in-1 Metal Superyard - 144 inches Long Play Yard: Create an extra-wide gate or a play yard. Hardware mount or freestanding. 6 panels, 10 sq. ft. enclosure (30" tall, Beige) https://www.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_cp_apa_i_VoJFDbPZST87Q
We had it over a foam mat. Now that we moved and LO is older, we have 3 panels with the gate mounted to seperate the living room from the rest of the house. Keeps toddler in and pets out.
Not single but at that age we had a big pen she couldn't get out of. Like this: https://www.amazon.com/Metal-Superyard-North-States-freestanding/dp/B000U5FOT2/ref=sr_1_18?keywords=baby+pen&qid=1552874295&s=gateway&sr=8-18 Got mine hand-me-downed from my brother's kid but you might be able to find one second hand.
I wouldn't recommend it. I have a 3ft opening with a gate like that, and the pressure mount does not withstand stress very well. We finally took it down because our 2 year old knocked it down, but it was never that stable to start with. The issue is with how those extensions hold together, it makes the whole thing really wobbly and you either don't tighten enough and it slips off at the ends, or if you tighten securely, then the joints between those extensions bend under pressure.
I'd recommend something like this - it's very sturdy, and it can extend beyond the opening to either not need drilled-in securing to walls, or stand on it's own. We have ours in curved shape to block a large area (basically one end of the living room, staircase and the area underneath it) and even with the adventurous 2 year old it's quite stable.
I was not willing to keep my infant/toddler stuck in a playpen, so I put up a play yard (this one: http://www.amazon.com/dp/B000U5FOT2) such that the big kids and their small toys were sectioned off in half the play room. The bigger kids can choose to go off in their own small area, and the baby/toddler was still free to use the rest of the living space without being unnecessarily contained
I ordered two 6 panels because they were the same price as the 8 panel at the time. play area I love how tall is is. We have them connected so the space is large and there’s two ways to get in. I liked that I could attach it to the wall if needed. I would recommend this style.
My parents have this cloud castle at their house
It’s cute and easy to open up. It’s not as tall and when my guy was little he would stick his leg through the space and then roll over. This could have easily resulted in an injury if we were not there to help him. I wouldn’t recommend it.
For travel we have a pop up play yard and a pack n play.
Yeah, this sounds doable.
This might be an option, if you wrap it all the way around the metal part to a wall: https://www.amazon.com/dp/B000U5FOT2/ref=cm_sw_r_cp_apa_i_EhExFbKH82VR8
We have an awkwardly wide space that needed to be blocked off while still allowing bathroon access. There wasn't a straight line across so we put in this gate because the mounts allow for quite a bit of angle: https://www.amazon.com/dp/B00FLXBJ92/ref=cm_sw_r_cp_apa_i_9cExFbZEG0PSN
Alternate solution for those of us with 100$ to burn
We used this gate around my desk area until our little guy was about 2. Now he just leaves it alone... mostly.
This wouldn't work for you? Works great for me. https://www.amazon.com/dp/B000U5FOT2/