I put it together by myself (35 year old woman) and only recruited my 6 year old to help me hold things twice. It took me maybe 90 minutes or so. Very easy. We put a 10” thick twin sized tuft and needle mattress on the top, there’s just enough space to tuck the comforter down around it on the sides and bottom and maybe 1” gap that shows in the back. We plan on covering the back with pillows anyway. We put a regular pillow top twin mattresses on the bottom and it fit perfectly. Honestly you could probably fit an 11” thick mattress on the trundle without any problems. Our mattress is roughly 10.5” thick and has a mattress protecter and sheet on it and there’s probably an inch of space above it.