Happy anniversary. I would definitely leave bub with your mum and go enjoy your night as a couple. My little one is 4 months too and since she was 2 weeks old I left her every Friday and Saturday night with another care taker so I can spend time with hubby as a couple sans baby.
Also my four month old is already on stretched feeds. She drinks at about 8pm and then falls asleep till about midnight and then wakes up for another feed and then wakes up again about 5-6 hours later. So if u are able to stretch the night feeds out, you will have the 4 hour window frame to go out while baby sleeps.
Also with regards to bottle, what bottle are you using? I swear by the comotomo bottles. Have you tried them? They feel like breasts as they are made from silicon.
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