So happy with this purchase - no complains! Lucid 8” firm gel memory foam mattresses fit good on top and in trundle. Purchased the XL twin as other reviewers suggested for the top, but the fit is a bit tight. I’d go with the 8” standard twin and a 6 or 7” mattress for the trundle if I was to order again. The thinner trundle mattress would allow for it to roll under with more than just a fitted sheet on it.