Sounds like you could use a "sock calculator
". Go to this link and follow the directions and you have everything you should need to help you knit whatever size sock you want. The calculator uses data that you provide -- stitch guage, shoe size, man/woman/child, etc. -- and works out the details for you, like how many stitches to cast on, how long to make the leg, how many stitches to use for the heel flap, how long to knit the flap, how many stitches to pick up for the gussets....
Take a look and see what it tells you. And if this calculator doesn't work for you, search on Google for "sock calculator" -- there are several out there and maybe one of them will work better for you!
Hope this helps! And happy knitting!