I got it off of Amazon a couple years ago.
Doctor Who Bad Wolf DW 4" Die Cut White Vinyl Decal Sticker for Car Automobile Window Bumper Truck Laptop Ipad Notebook Computer Skateboard Motorcycle https://www.amazon.com/dp/B00J0FSSE6/ref=cm_sw_r_awd_2WzGvb06B3CWF
I use a dog seatbelt that attaches to the latch system. You can pick what length you need.
Sorry in advance if the formatting is bad. On mobile.
Leash Boss Dog Car Seat Belt Restraint - No-Chew Heavy Duty Car Seatbelt for Pets - 5 Sizes - Coated Steel Rope to Prevent Chewing https://smile.amazon.com/dp/B073BFVKM2/ref=cm_sw_r_cp_api_glt_fabc_J7N990B0QB2X0FF9A4GW?_encoding=UTF8&psc=1
I bought them off Amazon. Search for Set of 2 Universal-fit Hawaiian Front Bucket Seat Cover - Blue Hawaii Hibiscus Floral Print
this should be the link: https://www.amazon.com/gp/product/B000VIIX5K/ref=oh_aui_search_asin_title?ie=UTF8&psc=1
after lifting my JK and putting 33s on it (total amount raised was 6inches) and having back surgery I couldnt lift my 180+lbs mastiff in and she wasnt keen on making the leap. I got one of these and with a bit of training (say ride and have a treat is all her fat ass needed) it works like a charm. Telescopes down and is held in place by the tail gait with a bungee through the built in handle
This one, with a seatbelt car restraint. It has a big handle on the back which is nice if I want to grab it.
EXCELLENT ELITE SPANKER No Pull... https://www.amazon.com/dp/B07FJM8Y6D?ref=ppx_pop_mob_ap_share
We’ve got his harness, https://www.amazon.com/ICEFANG-Tactical-Harness-Military-CB-Molle/dp/B078N3JYW1/ref=mp_s_a_1_13?dchild=1&keywords=large+dog+harness+no+pull&qid=1597615459&sprefix=large+dog+har&sr=8-13, and a dog seatbelt that has elastic portion that helps slow him, instead of a static jerk if we were to get in a wreck or have to stop quickly. We’ve had no issues with him getting tangled in it. We also only use the back D-ring instead of the chest D-ring. If he were to fall out, his weight would be supported by the harness and he wouldn’t slip out the back or hit the ground. Overall, it’s been a great system for us. Ps he’s 75 lbs for now.
I use this one.
I love it. It’s also a booster seat, you adjust the height so they can see out of the window and windshield. It comes with a seatbelt teacher that you can attach your dogs harness so they can’t jump/fall out. The lining and cushioning comes out super easy so you can wash it. I’ve had it for years and even with my doors off most of the time, I have zero concern he will fall out. It’s really easy to put in and take out too, but I usually leave it in unless I have a passenger. My little guy is 11lbs and has plenty of room to lay down in it also. Honestly can’t recommend it enough.
Harness + Seat belt clips (Like This).
If I have the seat out (90% of the time since its a 2DR). I use weight rated carabiner's to clip the seat belt loop to the seat holds.
Got one of those for my Newfie, he's fat ass is too tubby to haul himself in without it. Might help
There are seat belts you can get for dogs relatively cheap!
Edit
Vastar 2 Packs Adjustable Pet Dog Cat Car Seat Belt Safety Leads Vehicle Seatbelt Harness, Made from Nylon Fabric https://www.amazon.com/dp/B014W40TSW/ref=cm_sw_r_cp_api_4QU-ybJ29EY8F