Hi Al,
if you like your m° SL137, then your only choice is between Tribal Radix 128 and Tribal Radix 135 ...
Please don't think it's just the length that makes the difference. Board shape is MUCH MORE than just the "numbers" you see, such as length/width/volume/weight. As an example, the CarbonArt boards I used to sail up to 2013 and the m° SL boards such as yours, had about the same length but very different behaviour. In my experience older '08 and '09 CarbonArt and the m° SL were somewhat comparable, while newer CarbonArt (I had '10, '11 and '12) were pretty much different. More recently I used '21 FMX boards, the smaller ones (98 and 108) are 235 cms long, the Radix I am using now are 239 (and the most recent Radix are 237 now), but TOTALLY different on the water. Much more than one would expect by the numbers only.

_________________
.g.e.o.
Tribal Radix 110, 128
S2Maui Venom '25 6.7, 7.5, 8.2
Tribal Slalom Mk3

To complete my previous post.
My Tribal Radix 128 behaves very closely to the m° SL137 I owned and used from '14 to '20, BUT without its shortcomings. Same is for the Radix 110 compared to the m° SL112.
The Radix are lighter, feel more lively, plane even easier, accellerate quicker.
I will not discuss speed, as their common designer Chris Lockwood clocks over 40 knots on any older m° SL or Tribal Radix size: all of them, m° or Tribal, are evidently more than enough fast for most of us if not for all.
On the other hand, the Tribal Radix kept all of the nice sweet behaviour of the m° boards, with incredible control and huge (probably even better) range. My previous m° SL137 felt better with a 7.7/7.5 (S2Maui Venom) than with 8.4/8.2, while my Radix 128 feels same as nice and more compact with 7.5, and better suited than the m° with 8.2. Same story with the Radix 110 vs. m° SL112: both are just superb with 7.0/6.7 sails, but the Radix does much better than the m° with 7.7/7.5. So I'd say that the Radix kept the ease and control of the previous designs in their higher range, and got better in lesser winds.

_________________
.g.e.o.
Tribal Radix 110, 128
S2Maui Venom '25 6.7, 7.5, 8.2
Tribal Slalom Mk3