I got these Spence Polysorb Total Support #3 inserts (Women's size 9.5-10) to use in my Ugg-type boots. I usually wear a 9.5 in shoes.
My custom orthotics are only 3/4 length, and they wouldn't stay put in the sheepskin boots. The Polysorb inserts are full-length and provide very good support. I had to trim a little from the end of each insert to fit the boot properly, but they are great now and don't slide around.
Haven't tried them in any other shoes, but I imagine I would have to trim them much more for "regular" shoes. They run true to a size 10, and are fairly wide.
They are much better than other over-the-counter inserts I have tried.