Hi there,
As Connor mentionned, wild camping if officially prohibited but not enforced; you must however avoid doing so in any area registered as natural or wildlife reserve. Otherwise, if you stay just one night, it should be OK...
You will find here some more details:
http://www.sac-cas.ch/fr/environnement/sports-de-montagne-protection-de-la-nature/camper-bivouaquer.html
A nice place where you can mix both an "easy" walk and camping is the Lac de Taney - Grammont. There is a small campsite in front of the small lake, and from there you can walk all the way up to the Grammont, from where you will have an amazing view on the Léman.
To reach Taney, you can start walking in a place called "Le Flon" (which is not in Lausanne city center!):
https://maps.google.ch/maps?q=Le+Flon,+Vouvry&hl=en&ll=46.337417,6.854868&spn=0.016089,0.042272&sll=46.340084,6.850834&sspn=0.016088,0.042272&oq=Le+flon&t=h&hnear=Le+Flon+Vouvry,+Valais&z=15
Another easy option is the "Dent de Jaman", above Montreux. You can reach it after a short walk (1h30... ;) ) from the train station called "Les Avants", on the MOB line, that starts in Montreux.
Cheers!