I assume thats the Oasis TA Orla? We're on that too, but we are doing the one week cruise before as well, so doing a B2B. However, we are staying in Miami for 4 days prior to getting on Oasis. We have plumped for the Holiday Inn at the Port of Miami (on Biscayne Blvd). Not the cheapest, but you can get breakfast included, the Bayfront Park is right across the road which also has a 'marketplace' and an observation wheel. There is a Metromover station about 100yds away, which gives free travel round the area, together with a network of 'trolleys' which I believe are free and a HOHO bus stop right outside the hotel. See what you think.
Simon