In reply to Julian Prieto: Snowshoes will be fine. I used them many times to get to routes in places such as the Tacul before I learnt to ski, and even after fresh snow, they work.
One tip: do not be tempted to walk down the Vallee Blanche after your route. It's a long way and gets very wet towards the bottom in spring. Going back to the Midi is a slog, but in the end, easier. Best to stay at the Cosmiques and do more than one route.