We plan to build one but waiting on the price of wood. Right now our 2 almost 3 year old just had the basic metal bed frame that we had on that bed before and it’s not been an issue. I did buy the pieces for under the sheets to keep her from falling out and they are worth every penny in my opinion. Great to cuddle into, she can’t roll over them (I can’t roll over them), easy for her to climb over and easy for us to climb over when we fall asleep in there. Also it’s a 2 pack so we have one on the wall side, she can’t kick the wall and so far no toys have gone over the edge.
Edit: link
Milliard Bed Bumper (2 Pack) Toddler Foam Bed Rail with Bamboo Cover and Non-Slip Hypoallergenic Water Resistant and Washable Cover; Bed Rail for Toddlers, Kids, Adults and Seniors https://www.amazon.ca/dp/B07B3VZQNG/ref=cm_sw_r_cp_api_glt_i_7CM10KN9BSSDCFJQHFS1?_encoding=UTF8&psc=1
We bought a very simple wood iKea bed frame (and mattress) and cut down the legs, which was fairly easy and much more affordable than some of the branded floor bed frames. We have a foam bumper that goes under the mattress (amazon - set of 2) and like it a lot, very effective and not as bulky or annoying to get around as railings.
We actually used a long pillow instead of a rail. Something like this (we have a different brand that's no longer available):
https://www.amazon.com/Milliard-Non-Slip-Hypoallergenic-Resistant-Washable/dp/B07B3VZQNG/