It can vary widely. I've been to Clearwater in January with daytime temps in the upper 70's and little breeze - lovely for walking the beachfront. I've also worn winter coats in FL in January. If it's too cool for the beach, there are still a ton of things to do in Florida.
Ocala is less than 2 hours north of Orlando, up I-75.
Silver Springs is reportedly worth a full day's visit, between 2 nights in the area. In nearby Dunnellon, rental canoes are available at the
State Park on the Rainbow River (a gorgeous, springfed, clear-as-an-aquarium river, where scuba divers practice their skills) Ocala is home to many thoroughbred horse farms.
Homosassa State Park and wildlife refuge is about 2 hours northwest of Orlando or 2 hours north of Tampa. There, you can see manatees and other wildlife, if that interests you.
Certainly, there are plenty of things to do in the Clearwater/Tampa/St. Pete area. Besides Busch Gardens, there are many smaller land attractions, golf, boating, deep sea fishing, sightseeing charters, museums, etc. Honeymoon Island State Park is not far away, if you want a natural beach setting.
If you end up on the Atlantic side, Daytona is about an hour and a half away from Orlando. Besides the beach, there's the Nascar Museum, some shows and smaller attractions. Down by Cocoa Beach, NASA's attractions are mostly inside (bus tour and inside buildings), so that would still be okay in cold weather. If it's not rainy, you'd be near the beachfront there for walking.
Have you considered staying the Orlando area to visit some of the quieter attractions? Downtown Orlando offers plenty of cultural arts and a great Science Center. There are some "Old Florida"
nature parks in the general Orlando area too. And of course, there are smaller tourist attractions & dinner shows that you may not have seen before. HTH!