This is just a thought I've had lately - it appears that felted patterns have the same number of stitches as the unfelted ones - or darn close. The difference being that you use double strand of 100% wool yarn and size 11 or 13 needles instead of single worsted strand and size 7 needles or so. The felted hats seem to have the same number of stitches as unfelted, same with socks. I'll have to experiment!
Felting will shrink your project by about 1/4. So if something is 12 inches across assume it will be about 9 inches when you are done felting. But, you can stop the felting process anytime when you have reached your size desired. Another suggestion is to check out other felted hat projects and just add the ruffle type brim to it before felting.
Don't forget ..... it will felt more long ways than width... so it isn't always just a matter of using bigger needles and bigger yarn. The FT Ballerina slipper pattern ... the foot length is almost 24 " for ladies medium ( 9" long after felting) but not three times wider that your foot.
I thought I was going to felt a square for a pillow once .... it didn't end up a square... it ended up a rectangle!