Ah op, I'm just back a month as well and honestly the thought of it was so much worse than the reality at least in my case.
I started ds into nursery 3 weeks before I went back and honestly it helped a lot because he was settled well by the time I was actually going to work and I'd got used to him not being with me 24-7. So if you are planning on using some form of childcare I'd recommend starting a little bit before.
How long do you have left of your mat leave?
I tried really hard not to put pressure on myself to pack in loads but just to really enjoy and soak in the little joys like contact naps and playing in the house or cooking and eating long breakfasts together or having snuggles in bed before we started the day. And now I really look forward to those same moments at the weekend.
I'd be honest with your manager about how you're feeling so they can support you. I found I was rustier than I'd anticipated and even now a month in, there's things I would have done before without thinking twice about it that make me really nervous now or that I need to really concentrate on, so have a bit of grace with yourself, don't rush into trying to be straight back to who or how you were before and expect a little bit of stretching. Your brain is learning how to tackle a whole new set of responsibilities and pressure on top of everything else you've been doing in the last lot of months and it is a lot and it does take time.. expect that and let yourself ease into it.
Use your annual leave accrued to phase your return if you can. I was exhausted the first two weeks back and I was only in 3 days. I'd also have a think about any flexible working requests that could help you find balance.
Talk to your partner and your friends about how you're feeling and know you're not alone. There were a few points I was thinking how will I ever do this, but now I'm back ds is LOVING nursery and it feels good to have something that's for me again. It's hard and you're allowed to feel sad.