I lived on Big Pine Key for about 4 years (15 years ago),
30 miles north (like it could be south, or east, or west) of Key West.
I would plan to stop at Bahia Honda state park, it's 6 miles or so north
of Big Pine. Very cool beaches and you can camp there. Couse if your
going soon it would be to cold to swim. As I remember there are 2 beaches
one on the road/bridge side that sloops down fairly quick. I liked the east
beach, very slow sloop...you can walk out on the water a couple hundred yrds and still be knee
deep (in some areas) and gorgeous. Used to take the kids there when they
were little. I would google it, don't know if it closes or anything.
Beware the traffic, as it was 15 years ago I don't remember heavy season vs
light season but there were times it was bumper to bumper going south on big
pine...used to pismeoff...darn tourists