Wow, you have so many possibilities it's hard to narrow it down. Here are some of my ideas based partly on first-hand knowledge and partly on years of research about diving the Indian Ocean islands:

- Most of the reefs in the area suffered badly from the coral bleaching event and are still recovering.
- Mauritius is very friendly and laid back with a reasonable variety stuff to do apart from the beach. But the reefs are not the best and usually require a fair boat ride to get to the quality dive sites. Also check the weather for the time of year - the best side of the island depends on prevailing winds.
- With its huge granitic boulders, against the turquoise sea and blinding white beaches, the Seychelles is without a doubt a one of the most physically gorgeous places on earth. Real must-see-before-you-die stuff. Has many opportunities for shore diving and sites that are a short distance from shore. But I found a second trip exposed the charmless side of it too clearly (numerous distressed feral animals ignored, poor service, so little culture there's not even a bookshop). Also very pricey. That's a conscious strategy so I'm surprised you are finding reasonable rates.
- Mozambique is high on my wish list. Everyone I know who goes there gets to see whale sharks! There's a variety of lodging from very expensive to rustic. Also need to take a boat to the reefs. By all accounts a very "authentic" feel with the local lifestyles little affected by tourism as yet.

At the risk of adding to the confusion you could add:
- Madagasar. Loads of interesting things to see and do - the most fascinating fauna and flora - and some wonderful reefs. Also not spoiled by tourism but distressingly poor. French influence persists pleasantly.
- Zanzibar. Wonderful diving and a fascinating cultural experience - Middle East meets Africa (it was ruled by Oman for a long time) and creates a unique culture.

Once you narrow your choices I might be able to suggest places to stay. (I can't think of any hostelry that is a desirable destination in and of itself.)