Hmm.....You can always cup the little baby and remove him, then try the heater and see how it does. It may work on the lowest setting, and if its adjustable(which I assume it is of course)then it should hold pretty steady. If it doesn't work though or if you're really too paranoid(which I TOTALLY understand), just something 25 watt thats adjustable with a thermostat should be okay I'd think.
I just ordered several of these: http://www.ebay.com/itm/-/2710315149...E:L:OU:US:3160
And they actually work very well, cheap too obviously, and nice and small size-wise. They take a couple of weeks to come in though, which is the downside....but I thought I'd toss it out there for you anyway.