On boats with outboard shrouds, the headsail size is limited by the leech hitting the spreaders and/or diagional shrouds. Normally this happens around 110%, plus or minus 5, depending on the boat. You sometimes CAN go slightly bigger than your existing sail, but you WILL NEED to have a sailmaker involved to precisely measure, design, and cut the new sail. You need to keep the sail off the rig.
No one here can help (except maybe Bob from NP); because even if you know a workable LP, it's ALL in the design.
Headsails are normally cut with negative roach (hollow) to keep the leech from fluttering; having your new sail designed with less/zero hollow and vertical battens can often add several square feet.
In any case the increase will be small, and most noticeable on performance boats sailed by performance minded sailors. Everyone else will get bigger bang for their buck with a Code 0 or a reaching sym.