What about a plastic motorcycle/ATV ramp or pet ramp?
PetSafe Happy Ride Folding Pet Ramp 62 Inch Portable Lightweight Dog and Cat Ramp Great for Cars Trucks and SUVs - Side Rails and High Traction Surface https://www.amazon.ca/dp/B0016HNU12/ref=cm_sw_r_cp_api_glt_i_XPNQD934B4YFTPVMB5XV?_encoding=UTF8&psc=1
https://www.amazon.com/gp/product/B0016HNU12/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
I got this one. It's an actual ramp with a not too steep incline so he doesn't have issues and can't really fall off it. Only took a week or so for him to use it 90% of the time when he gets off the bed.
On Amazon PetSafe Happy Ride Folding Pet Ramp
I used this. I trained my dog to use it by walking her back and forth while it was flat on the ground. https://www.amazon.com/PetSafe-Solvit-UltraLite-Portable-Lightweight/dp/B0016HNU12
I used to work on a veterinary specialty orthopedic team and our patients and their owners constantly dealt with this issue. Many would purchase ramps from Amazon to help with loading and purchase a harness with a handle to assist their doggy in and out of the car. It seemed to work great and was safer for everyone.