Le Bourg d'Oisans should fit the bill.
Alpe d'huez can be done in a morning or afternoon. As can Les Deaux Alpes
Galibier there and back in a day no problem at all.
Col du Coix de Fer and Col du Glandon in the other direction again easily in a day.
Lots of other lesser known rides in the area as well. Of which I highly recommend the ride out to La Berade.
The Bourg tourist office has maps online and in print for free.
Would you like some accommodation advice as well?
And finally if you are really fit you could alsways do the Marmotte course. 😯
But, in spring will you have enough daylight hours and there will be a high risk of the cols being closed by snow.
The last time I was there in September the Galibier got closed one weekend by a meter of snow.