Better do it now. I'll forget to come back in a few weeks. I'm finding it to be soft, but theres a very dense foam layer at the base so it doesnt all collapse down to the bed slats, cant feel those at all. I'm a very large person and I find it just right for my bulk. A thin person might find it to be too firm, a larger person than me might find it too soft. I do have difficulty changing position but I dont believe thats anything to do with the mattress, I had the same issues when I had my other sprung mattress. Initially I found it a bit grippy because of the memory foam layer but its not an issue. Overall I find it very comfortable and as I said in my other post, I am getting out of bed pain free for the first time in years.
I wouldn't muck about, if you want to try it out you get to do that for 120 nights and if you dont like it, they will give you a full refund (assuming, I suppose, that you havent ripped it to shreds or crapped on it!!) So really, you can't lose. The $350 off on double, queen and king has been extended for March so not much time left to decide. They might well decide to extend again but they already did once, dunno if I would depend on that.
I love mine. Now I've had it for 3 weeks and at this stage with every other mattress I have ever had, I've been bitching about this or that. Not this time. When it wears out, if I live that long, I'll do it all again. Planning to get one for the spare room.