For example:
Bewildered, he looked only to see his, wooden? floor.
How would I do this without throwing a question mark in the middle of the sentence?
First off, what is required is that this be told in a close point of view, because it only makes sense as the jumbled thoughts of the viewpoint character.
I would phrase it as:
Bewildered, he looked only to see his — wooden? — floor.
I hope it is clear in context what is meant by "his" because normally I would expect someone to know the material of any floor describable as "his."
I would make the question mark parenthetical:
Bewildered, he looked only to see his wooden(?) floor.
Because it is a parenthetical observation within the context of the sentence.