Memory Foam Seat?

You can tie any cushion you prefer to the seat. For example, put the cushion you like in a pillow case and use string (I find kite string is very useful for many things) to tie it to the seat bottom or the seat back. Since the cushion will be small compared to a pillow, you can tie each corner of the pillow case into a small knot. Then tie the string to the corner knots as needed and you have a cushion with straps. Or use the small bungee cords to grab the corner knots and then to the truck's seat.

It is OK to make things fit your needs instead of buying someone's over-priced truckstop version.

 

I found a cheap knockoff of the purple "egg crate" cushion on Amazon. It came with a neoprene covet. Since it is silicone it is both firm-ish & durable. I had a memory foam seat back cushion with a lumbar curve that worked well. I suspect sitting on a memory foam cushion, the cushion will wear out quicker than the Purple brand name type cushion.

 

This amazon item shows what I found to be durable and comfortable enough for me. The purple cushion is silicone and the cover protects it. My one complaint, and it may not apply to you. I am hot natured. I like temps in the 60s or less and feel too warm in the mid 70s. Sitting on the cushion I have causes a certain amount of "swampiness". I'm not saying the cushion/neoprene cover is causing more swampiness than I would have on some other cushion, but the cushion/cover don't cause less swampiness than no cushion. It's probably my issue and not the cushion. Since the silicone and cover on my cushion don't absorb moisture scuba diver wetsuits are made of neoprene, the cushion/cover don't smell worse and worse over time. I suspect a memory foam cushion, if I used one, WOULD absorb more and more moisture.

BTW, the most common memory foam seat cushions on Amazon that share this sort of shape all seem to share a similar over-engineered shape with deep contours and a cut-out under your tail bone. IMO, that's just a dazzling gimmick to suggest super geniuses designed this thing so don't mind paying lots of money. They may work well for you. I don't know.

 

Can't help you with a name brand but I have a memory foam cushion off Amazon about 2 years ago and it's a night and day difference. At the very "rear" it has a U cut out so you're not sitting on your tail bone.