Ken has pretty much covered most of what I would have suggested.
Getting a larger (wider and capable of carrying a larger fin) board is not going to get you
much in terms of early planing and quality time on the water in lighter winds if you stay with the 7.5, esp. at your weight.\
An 8.5 m2 free race rig will buy you alot in terms of early planing and somewhere between 8.5 and 9.5 you will run into a sail size "threshold" where larger sails won't get you much gain (unless you get a really wide board similar to a formula).
Again, Ken has pretty well covered the attributes of the 133 and 144 Futuras.
If you were to get a 9.5 m2 rig then a 150 liter + Futura or iSonic makes a bit more sense.
As Ken suggests, give us a better idea of your skills and actual windspeeds and water surface conditions and we can refine the answers here.
Hope this helps,