Get yourself down to your local pool and hit the water!
It's great exercise, working ALL your muscles, and you won't get too overheated!
If you like, there are exercise programs for various fitness levels at most community pools, and aquasize is fun! Even just doing a few laps then resting, and then heading off again helps. Take the kids or hubby to make it more enjoyable. (I go with my GF all the time. we have a great time "racing" with her taking about a half pool headstart! I get a good cardio workout, and she goes at her own pace. Great for both of us.) even if you aren't the best swimmer, you can wade back and forth across the pool's shallow end.
Give it a try and let us know how you make out.