With all due respect to Ron Mangus, memory foam and gel pad are hyped as solutions to seating problems, but they're also very expensive, and will not give you any more support than regular firm seat foam. Eventually, all foam will compress, and then you are feeling whatever is supporting the foam you have used. Ideally, you would like springs under the foam because that will let the whole assembly flex all at one time. Now I know that you have height restrictions in the "T" bucket, but using something expensive will not necessarily make the seat better, only more expensive.
No one lives forever, the trick is creating something that will.