The best thing I have found for sliding under a car is an old sign banner or best yet is flexible sign face material called panaflex by 3m. If you go to a sign shop they will likely have some scrap to give you. It is a smooth tough vinyl surface you can roll under the car and slide around on. when you drop something, you can easily find it, oil wipes off it easily, and you can roll it up and put it in your trunk. Creepers are useless on gravel driveways and the side of the road. When I was 16, that is the only spots I had to work on my cars. I wish I had some back then. Next best is Coroplast, it is like plastic cardboard used for sign making, it makes a great creeper, but you can't roll it up like the banner material.
Be a hero & get him & you a lift. Best bang for the buck. I hate creepers. Tripped over on & dis-located my left shoulder when it didn't want to fall down with me & got hung up on the door of the truck. That was two years ago & it has been dis-located 6 times since. A hoist is way cheaper than the medical bills & pain. Oh I have a hoist but wasn't were it was at the time. Mine is a rotary 4 post but anyone will do.
I've got a Craftsman "Professional" creeper (garbage), and a "Bone". And I still prefer those interlocking foam mats that you can get at Sam's Club or Walmart. 24" x 24" and about 1/2" thick, you can link several together, and provide some cushioning. They work great, and they're cheap.
I have this....Caddy of creepers IMO, Ive had it for years! Low profile, but nice big wheels and HD frame Ya might try here too for other options, Ryan's other site..