Santorini is doable in a stop over. Blue star ferries (I think they were/are called) hop between islands. On paros I know there’s couple of companies run trips to Santorini that do a tour of the usual haunts (Oia, Akrotiri, hot springs, volcano etc) they were reasonably priced last time I was there. Didn’t like Santorini itself but the ruins at akrotiri are well worth a trip if you’re into that kind of thing. One of the trips we went on included a boat trip where you could jump from the boat and swim to a secluded beach for a picnic (or you could be boring and take the outboard to the beach!)
Definitely something we like and plan to do on our holidays.