Hi Petite.Violette - salut!
If you want all of that in one place, I'd recommend Jinja 'Source of the Nile' approx 3 hours east of Kampala.
Lots of v relaxing places by the river Nile + excellent coffee shops in Jinja town. Jinja also has enough bars and clubs to keep you busy socially for 10 days 
Jinja is the adrenaline capital of E Africa: white water rafting, quad biking, horseriding, fishing, birdwatching, sundowner cruises, sailing and much more.
See one of my stories on my blog 'Diary of a Muzungu' -
Feel free to message me for more ideas, here or via my blog and Facebook page of the same name.
Jinja was once the industrial capital of UG until Amin expelled the Asian community. It now has a 'shabby chic' appeal: interesting old buildings, lots of colourful craft shops and markets, potholes in the streets that match Bujumbura's(!)
Places to stay I recommend in Jinja include:
Nile River Explorers - Camp or Hostel
The Hairy Lemon
Source of the Smile
Gately Inn
Kingfisher Resort
The Haven
Bon Noel et amusez vous bien!