It is best to get the proper sized frame but frames come in only a few rather narrow sizes and humans come in all kinds of sizes. Adjusting the saddle to a little more forward position with a seatpost that has zero setback would be acceptable given that you've already shortened the stem and are still experiencing fit issues. Sliding your saddle too far forward starts to mess with the front/rear wheel loading of the bike and can mess with the handling. But just don't go crazy. Try the inexpensive post I linked to above first, put you saddle in the middle of the rails or even pushed back a little. Then experiment with the moving the saddle forwards and backwards. It might take a few rides to get the position dialed in.