SSL across whole network, on mapped domains, including new signups

Hi There,
I'm looking to add SSL as standard to all sites on my network. I currently have about 150 sites, and around 90% of those have mapped domains. Furthermore, We are getting around 20 new signups per month, these start off as subdomain sites (i.e. example.skizzar.com) and once they are built, the user can map their domain in (we use your amazing domain mapping plugin for this) - I would like these cases to be automatically https, whether it's a subdomain or mapped domain.

Is there a way that this can be done - can you recommend any SSL certificates and settings I would need to make sure my whole network is served over SSL.