Best 3 month old sleep outfit?

I have a 3 month old, and it gets pretty warm in our apartment. She likes to be swaddled (otherwise her startle reflex keeps waking her up). I don't know how to dress her for sleep. Is it ok to still swaddle her? Do they make a onesie style swaddle? I have a 100% cotton swaddle for her, and it seems to work- But on the 85*-90*+ days/nights, I don't want her to be too warm. We do have a fan on her at night when it's warm (It doesn't blow directly on her, just creates a breeze over her). Wasn't sure if a diaper and swaddle would be ok? She has a waterproof cover on the mattress as well, so that tends to keep in some heat. Any suggestions would be appreciated! :)