Swaddel/sleep sack, how to keep LO warm at night?

krismt

My 8 week old really seems to need to be swaddeled to go to sleep, but she is wriggeling free of it in the middle of the night.  To the point that if she goes down at midnight I may be up at 2 re-swaddeling her (she'll make a bunch of noise and be moving all around, then re-swaddeled she quites back down & sleeps peacefully), and then up at 4 when she really wakes up to feed her.  We have a sleep sack we could put her in, but it won't keep her arms down, which seems to be necessary for her to sleep well, all the moving about cann't lead to much rest. 

I am also concerned about her staying warm enough at night....

suggestions?  thoughts? ideas?