Hey Teach, same boat here, we just are thankful for longer stretchs of sleep if we get them
The solution i use to wash MJ is calandula flower tea and chamomile tea diluted with water - never had any nappy rash, if the wee gets a big pong and she looks like NR may start i also add this to her bath.

the lavender sounds good, however i would like to know what she is mixing the oil with as babies cant have essential oils diretly onto their skin, so she must be mixing with something - could you find out Danni as i have lavender at home... ta