I got some second-hand boots with the inside sole worn down to bare. So I went to Walmart for insoles, and got the SofComfort Gel Comfort inserts. They are sized "Women's size: 5-10", which they obviously don't know that is a large range. I, a size 7-9, am finding these extremely uncomfortable. I believe the boots are a 7 or 8, and the inserts don't cover the whole sole. My foot also doesn't fit on the whole insert. The sides of my foot fall over, which is painful, and either my toes or heels will fall off, which is just as uncomfortable.
If you are a size 5 or 6, this would probably work for you, but not too useful for any size larger.