I would say Tignes/Val D’isare ticks many of your boxes.
Took me 11 hours from Calais in a sluggish old Transit.
Loads of Lake based activities as well as tennis courts, skatepark, archery etc. which are all free with a Tignes pass you collect from tourist information office.
Lots of MTB runs (it is a bike park) with lift access with a nice selection of greens and blues (more blue and red by UK standards I think). There’s also a green and blue from Val – my wife loved the green and is not a hard core rider.
Some nice walks too which can be accessed by the lifts.
Oh, and all the lifts are free too for biking and hiking.
For more experienced bikers it’s a bit bland (so folk have said on here) but was ideal for me and family, although I’m not a riding god.
PS – as it’s lift assisted make sure your insurance covers it – I used Dogtag.
HERE: http://en.tignes.net/what-to-see-do/do-something/summer