I'm in the wheelchair full time for 9 years now and I have an adjustable air filled seat cushion, luckily my 2 insurances paid for all of it. The MS Society can probably help you to find out more about getting one of those, maybe even financially. Those cushions cost about $500, for a darn cushion, RIDICULOUS.
Even with one of those I can't stand sitting in my wheelchair all day, so I spend most of my afternoons in my recliner on a piece of memory foam. That memory foam will probably be good to sit on in the wheelchair as well. - My caregiver rubs vaseline on my bum everyday, that makes it feel a little better too and helps prevent pressure sores. I hope this helps.

You're welcome LouiseWallwork. Sending hugs your way.

Hi I'm in my Wheelchair full time i to suffer from a sore bum. I have a Jell cushion which helps and I sit on a memory foam donut on top of the Jell cushion that helps a lot but i still have to lie down for a couple of hours. My caregivers rub proshield cream on my bottom which helps to prevent pressure sores.
Hope this helps kind Regards Brian in Somerset U.K.

Thank you all for your advice Xx