Cash VS Credit, Which Do You Use?

My husband and I are reworking our budget yet again right now, because he really wants a Sleep Number bed, but I'm not sure I want the extra payment.  Paying cash isn't even really an option right now, since we just bought a truck for my husband (and paid cash!!), and we're in the middle of the basement remodel.  We are going to have to buy a new bed soon, though.  Ours has two springs sticking out the side now, and no matter how many times my husband tries to fix it, they poke back through and end up ripping sheets.   Sheets are too expensive to replace every few weeks!

Anyway, when looking around for creative ideas of ways to cut our budget, I keep seeing people say that switching to cash is the easiest way to do it.  That doesn't work for my family.  We've tried it two or three times, and we usually end up spending MORE when we have cash, than when we don't.