138 if you want to use boots. They are bigger than straps and the xtra width helps. You can all so hold a lot more power down with them so a bigger board really is not bigger.
lets not forget that asylum is not a pure wakestyle board and has less rocker
i, personally, think that 134/40.8 will be more than enough for 65 kg even with boots
lets say 138 will gives a little bit extra low wind but, for sure, will lose in high end
i`m 75 - riding 134 Asylum, very happy with it
starting to go upwind with my 2012 RPM 10 in about 6 -7 m/s