My children are mostly grown up now (ages 8, teen to early 20s) but the only way to afford the baby/toddler stages of our family (on a standard salary) was for me to remain at home. I picked up term time work and sent my youngest to a nursery school age 3, paying a top up for wrap around care for the additional hours during term time. (Maybe Google your Local Authority to see where there are nursery schools near you, if you could consider term time only for a few years.)
Lifestyle choices included- older car, cheap UK holiday once per year, cheap days out such as the beach, park, museum, few meals out and virtually no spend on clothes/hobbies etc, minimal home improvements.
Being a sahm isn't for everyone, I'm just mentioning that the reality can be different than the expectation. Whatever you choose to do, you might consider it or pt work further down the line.
Overall I spent more than a decade at home. I studied for a degree through the OU to faciliate career development during that time.
And with two children you could downsize to a 2 bedroom house for a few years. My children really enjoyed sharing a bedroom until the teen years, at which point we made changes to enable this to happen. (Ours was a 3-bed we later converted to a 5 bed.)
Having another baby will almost certainly impact upon your current lifestyle, I'm just making suggestions that I haven't yet seen mentioned (admittedly I haven't read all 21 pages).