A new mattress changes how you wake up every morning. When you replace your frame and foam at the same time, you build a foundation that actually lasts. Aim for holiday clearance cycles like Memorial Day or Black Friday, when retailers push out old inventory to make room for new stock.
Get at least three quotes from local or online showrooms before you commit to one brand. Ask them directly if they can match a competitor's price for the frame. Once you have a final number, you can set up a simple repayment plan to get it paid off before the interest kicks in.
The 0% window is a deadline, not free money. If you have any balance left after 15 months, the bank will start charging interest on what you still owe at their standard rate, which is likely quite high.