Tanzania is superbly placed to combine a first class safari with a few days on white sandy beaches and turquoise waters of the Indian ocean.  Zanzibar and Pemba Island are a short flight from the mainland and are very easily combined with virtually any part of Tanzania.

There seems to be a received wisdom that you do your safari first, then hit the beach.  And it's true that while safaris are an exceptional holiday, they can be quite hard work.  You're on the go, getting up early and generally being quite active, so it does make sense to give your self time to recover after all this.  That said, there is no reason at all why you shouldn't leave work and get some steady rest for a few days before going on safari.

If you're really looking for an exceptional beach experience and Zanzibar sounds a bit busy (some parts of it are worth avoiding), then northern Mozambique is now very easy to comine with Tanzania.