I’ve read guest reviews with complaints about trundle beds. One problem is that many trundles aren’t really for adults but there isn’t a way to specify that except in the listing text, which guests will miss. Also, make sure whatever you buy is both sturdy and intuitive to use. If bunk beds are an option, they are also something to consider, but of course, they come with their own set of problems.
I’ve read complaints about double (full) beds as well, so if you can reasonably fit a queen bed instead of a full, do it.