twin mattress recommendations?

Hi,

I am transitioning my 2-year old daughter into a twin "big girl" bed. I just bought a nice, gently used platform frame with drawers underneath-- now I need to get a mattress. I have been searching for a good mattress (not too cheap, not too expensive). I believe her crib/toddler bed mattress is a Serta Perfect Sleeper (it was about $120 when we purchased in 2009). I'd love to hear about your twin mattress (brand and approximate cost). We are looking for something that will be comfortable and affordable.

Thanks,
Rebecca

Whoops, I meant that her crib mattress was a Sealy Perfect Rest -- the one recommended by BB.

bumping. My toddler jumped out of her crib this weekend. So we need to purchase a new bed soon.

Did you decide on a mattress? I need to get one for my DS and I've seen a mattress at sams but I'm not sure if its of great quality, the price looks great but not sure ... any advise out there?