I think you really just need to go for it one evening
Maybe do it on a friday or saturday evening when your DH can help out in the morning if she does wake up more than normal at night?
It took me ages to try Anna in cloth overnight, mainly because the nappies I had at the time were way too big for her still. But she didnt sleep any worse than with a disposable on - and still doesnt. I dont think they really care/notice what they have on their bum at such an early age, as long as they are not left feeling wet. And if she does wake up and you think she doesnt like it you can always put a disposable on then and put her back to sleep and try again another night.