Linens for sofa bed?
 

We just purchased a full-size sofa bed and I am not sure what bed sheets to buy for it. After looking at it opened up, I don't think that a regular full size fitted sheet would stay in place due to the thinness of the matress.

Any advice from sofa bed owners out there?

You can try the clips from BB&B to secure the bottom sheet.
They look like a garter.

If you want the sheets that fit look for Dimensions catalogue (google this) as they might have that size for sofa-beds.

Look for low profile sheet they are not as deep. Fitted Sheet I just tuck under.

Sofa bed sheets
 

There is a catalog/web site named Domestications that carries actual sofa bed sheets. I ordered some from them before and they work really well but do cost quite a bit more as they are specialty sheets.