Personally I'd only be able to do it at this age if he was asleep and would want to go and get him if he woke up. Fully understand your want to go to the gym though, are you able to go in the evenings and leave the baby with his dad at all?
@Laura I agree that’s how I’m feeling currently but maybe considering in a month or so. And yes I definitely can go in the evenings and will be for now think it will do me good to get out in the day although it makes me feel guilty to leave him!
Can you talk to the crèche workers? Is it a sign up and it's X amount of days or could you do a little trial? X
There are a few gyms/PTS in my area that do mum and baby classes in the daytime so you can take the baby with you. Maybe have a look into that as well?
Could you visit the creche and meet the staff first? See how it's run and what they get up to with the little ones. Might help make your mind up, as you say it's personal preference so no one can answer this question for you