Last year, I turned two skirts into laundry bags, by sewing the bottom edges closed. One was a skirt I didn't like the feel of, and the other just needed to be retired from my wardrobe. The fabric is strong enough. One bag has a drawstring and the other has a zipper, which is nice because otherwise it is rather difficult to get the laundry out.
Another project from a couple months ago was to turn a double-sized mattress into a twin size. It's an inner-spring mattress that's two or more decades old. The innards turned out to be very similar to the twin box spring I took apart one time; just no wood and less steel, and more padding.
I cut through the fabric and padding, and used a small screwdriver and pliers to pry off the metal clips holding the springs to the edge, and then wire cutters to cut the spiral wires connecting the springs.
The heavier steel edging was a little harder to deal with. I didn't want to cut it and then be left with no way to reconnect it. I came up with a scheme for bending each edge over to the other side--which didn't work because the width I removed from the mattress was greater than the thickness of the mattress, so they stuck out too far. I let it sit for a few days, and eventually figured out how to take up the extra with additional bends.
Then I started clipping things back together, crimping the clips I had removed back on with pliers. This went okay for the springs, and less okay with the rings that had to poke through the padding. They probably have a special tool for that at the factory.
I finished by sewing up the fabric with sturdy buttonhole thread. The mattress is a spare for now, and is currently on a free-by-the-side-of-the-road metal daybed frame, under another mattress.
I also, roughly a year ago, repaired a seam on my own mattress. I was thinking about replacing the mattress entirely, until I realized that it would be silly to replace the most popular bed in the house. I sleep well enough on it.