H.H.
My son's first bed was an ikea bed. The mattress is a little thin, but we have never had any trouble with it. It is foam, so we covered it with plastic. I thought it would be thin too, but is was surprisingly comfortable and we still have it and it's almost 6 years later.
We bought regular sheets and used them with no problem. The Ikea sheets don't fit any better then regular ones. The only problem was with the blanket- becasue the sides of the bed come up, the comforter doesn't lay that well over the sides of the bed.