I would recommend against getting a pillowtop mattress. What we have found is that the pillowtop gives out long before the rest of the mattress, giving us hollows in the middle. (We both weigh under 200#.) In terms of mattress brands, I like Stearns & Foster in their top and near-top of the line.
When our (expensive) king size pillowtop mattress started giving us problems, I decided to try a mattress topper. We got what (as I recall) is a 4" foam type mattress topper from Sam's Club for about $150 (back then; probably $200 now). We have had it on the bed for 4 years now, and it still feels great. The only thing we had to do about a year ago was turn it around head-to-foot. My brother was going to buy a new bed for himself and I talked him into trying the foam topper instead. It worked great for him too. It's been over 2 years now and is still fine. In both cases, it saved us a lot of money.
You could try purchasing a mattress and box spring set and putting the foam topper on to add some softness.
We have had no problems with the foam toppers in terms of odor, and I am very sensitive to smells.
For our next mattress, I am tempted to try one of the mattress in a box types. Here's a YouTube video of one:
https://www.youtube.com/watch?v=MqzZCn6PtT8
Edit: I should add we tried the Sleep Number years ago, at my insistence. Dh hated it so much he boxed it up (a lot of work!) and took it back to the store for a refund.
Edit 2: When I say mattress topper, I do *not* mean those egg crate type toppers. Ours is a smooth foam.