RE: iS145 vs. FT148
Yes, I'm sure the early planing characteristics of the S-Type 137 left quite a bit to be desired vs the FF or F-Type 158.
How heavy (weight) is your husband?
I'm not sure if it's the FF (F-Type) 158 or the 11.0 m2 Retro that's "feeling big" too soon.
If your husband isn't over 90 Kg. (198.4 lbs.) then the Isonic 145 at
88cm wide would certainly give him more range. Has he sailed your FF-138?
That would be similar to the Isonic 145 (width and length) but with slightly less volume.
If he finds your board to be too narrow to get planing early then the "compromise" would be the Isonic 155 at 95.5 cm wide.
Hope this helps,