This is the seat pad I use:
https://www.ebay.com/i/302356490626?...D1247620818448
Plus you get an extra lumbar pad. The front of the pad had a bumper that I tuck between the front seat and the gas tank. To hold down the back, I cut a bungee cord in half and thread it through a tarp clip like what Walmart sells:
https://www.walmart.com/ip/Scotty-Ta...&wl13=&veh=sem
The clip attaches to the seat cushion and the bungee hook hooks under the seat on both sides. A picture is worth a thousand words, but I don't think pics are working yet on this site, otherwise I'd show you my setup.
https://onpurple.com/seatcushions
these work great - I use the everywhere cushion
Be Careful What YOU Wish For