Your "bike inseam" isn't the same as your pant inseam length. To meeasure your bike inseam, stand with your back to a wall in your stocking feet with your feet about 10" apart. Shove a moderately thick book with the spine on top up between your legs and press it up firmly (not hard, you're not trying to hurt yourself) until it stops and against the wall simultaneously. Mark the top edge of the book on the wall (having a helper is a real plus). The distance from that mark to the floor is your bike inseam.
For example, I'm 5'9" and wear a pants inseam of 30" but my bike inseam measures 83.5 cm or 32.8". Use the bike inseam to help establish your initial saddle height and there are several formulas to get the first try. Refine it from there based on your personal comfort level.
As to choosing frame size, "standover height" is only a beginning. You don't want a frame so big you can't safely stand over the top tube but that's not the only important measurement. Top tube length is also a critical distance as it controls your reach to the bars.