The best sail for your older formula board would probably be an 8.5 m2.
This is the size limit for girls and women in Formula Experience, so it will
be light and easy to sail for a 60 Kg. sailor.
Any of the "free race" 8.5 m2 rigs, on a 100% carbon mast and a carbon
boom would be my suggestion.
Very light in weight, lots of low end power to get you going when there's marginal
Sailworks Retro/Severne Overdrive/NP V8/Gaastra Matrix are all good "free race"
designs and most of them can be found on the used market.
Hope this helps,