Haven't been to Mauritius but went to Cocos last season.
If you want to really relax, just kite, eat and sleep if you want, go to Cocos.
The place is amazing and there's other stuff to do but only of you can be bothered.
I was lucky with wind, 8m most days but it's not always as windy. Water is not super flat, but it's shallow without lots of reef etc and there is about an acre per kite most of the time.
Loved my trip to Cocos and may just go back this year.