I've been trying to figure the seat out also. I'm 5'8" with a 28" inseam but I weigh considerably more than you and the stock seat is perfect for me as far as height, reach to the grips, and knee bend. So I don't want a replacement seat to move me up, down, forward, or backwards and I don't care for a backrest. I just need more "cush for the tush" to eliminate the butt burn. The Air Hawk helps but isn't the final answer. I've been thinking of either an Ultimate or Russell, just haven't pulled the trigger yet.