My favorite one is a wondergel, which has since been bought by purple: https://purple.com/seat-cushions https://purple.com/seat-cushions It's pretty heavy but

My favorite one is a wondergel, which has since been bought by purple: https://purple.com/seat-cushions https://purple.com/seat-cushions It's pretty heavy but super comfortable. There are also inflatable ones you can get that are way more portable but also way less comfortable