Not sure I'd buy an extra product for that. They always have cushions on the international flights. There are usually some spares, too. I often wind up with two. Just stick one under your bum and you're good. I could also imagine just using one of the inflatable neck pillows which you then just don't inflate all the way.

Two more things.

It will be a very good idea to get up and walk around every few hours. Stretch a little, walk the length of the cabin a few times. Very few people do that. Why, I don't know. It helps a lot.

Since humans are built quite differently and experience things like blankets, beds and pillows quite differently, it seems like a very far stretch to infer from what someone else might like to what you might like. Perhaps in terms of product support, price and built quality, OK. But in terms of comfort, not sure.

Also, what you describe sounds very weird. I can only imagine some kind of condition or that you are very skinny (don't want to get too personal here).

If I were to buy a product, I'd go for the cheapest and less voluminous option first. See if that does the trick. Then go up from their. Perhaps you could also just take a big scarf that you fold together and place on the seat. This way you can use it as a scarf once you are there.

Enjoy Paris! Oh, and bring comfortable shoes because you will forgot all about your derriere once your feet start hurting because you walked so much.

Till