I am narrowing down my mattress but, was wondering, do these metal foundations fit inside my existing bed frame or will I have to look for a replacement box spring type foundation?
If we have to dump the head board and foot board I may just look at getting a King size.
I’m not sure which foundation you mean … can you link to it?
If you mean one of the 14" metal grid type such as this then it would normally fit inside a bedframe (as shown in the picture) but I would measure everything to make sure.
Many of them also have attachments for a headboard or footboard.