Every company I've ever worked for only offers SMP.
It utterly sucks. (i've just started mat leave today and am FREAKING OUT about our paycheck cut this month, even tho we've saved a 'topup amount). Ie, I've just have had a meltdown rushing round town comparing the cost of cotton wool to try and save a couple of quid a month in money madness)
It's tough, but try n stash as much in savings as you can beforehand - we got used to living on my DH's income and save mine, dipping into it when we had to to try and get used to the income we will be on now.
I found this website really helpful in figuring out my shortfall, and how adding holiday to the end of it can help with it. maternity.money/
Childcare costs TONS (mine is gonna be at least £900 a month for full time) so going back you're still on a lot less money unless you've got family / friends who you are happy to leave your baby with.
Things I'm using to help:
IF you've got any form of side job- you can keep doing that through mat leave if it's within your contract - tho i think you might need to have been working there for the 26 weeks before qual week etc. For example I coach sports, so will be going back to that from when baby is 3 months old (ish) to earn some small additional dollar.
Otherwise you can earn up to £1k without having to declare it to HMRC, which can help with some bits n pieces.
Started stashing 'an amount' each month already for baby - now we've got a cushion, and our regular outgoings include 'baby' amount each month as clubs and things seem to add up too.
See what your partner's work does (if applicable). Unfortunately my DH doesn't get paternity leave, but he is being allowed to take 2weeks off when baby arrives, so we'll actually in many ways be better off.
Good luck - I'm right with you. xx