I was searching for something I could fit my two 9 mattresses on and Im happy to say the trundle fits the 9 memory foam without any struggle. I wouldnt go any larger, and I dont leave a comforter on it (I might try to at some point, but I think thats where wed be touching the bedframe on top). But after the original daybed I bought broke during assembly I felt really stuck with the mattresses Id bought specifically because that model was taller. 
 So very happy with this purchase, it looks cute and feels sturdy. We havent tested the weight limit too much, but 510 man with 11 yo child and a large dog all sat together with no problems.