I'm 3 months in and to be honest I feel like things have just got a lot easier the past week or two. The youngest is 3 months, the older is 16 months.
If you can, keep the older one in childcare for a day or two a week. It means you can get some time with the new baby (the older one usually takes most of my attention when I have both of them), go to a class with them, get out for a coffee, do some housework, or just make a coffee and put your feet up when the baby is napping.
I think an up and under double pram is better at this age. I also have a side by side double which I'll use later on, but it wouldn't work now as the older one would constantly be trying to poke the new baby in the eye!
If you don't do it already, order most of your groceries online. And get amazon prime.
Take whatever help anyone is willing to give you. At the start, I felt like I had to things myself as this was our decision, but now I'm happy to go and see a family member for an afternoon, and maybe ask them to keep the younger one for half an hour while I take the older one to a rhyme time class at the library, or ask them to play with the older one while I feed the baby. I find they're actually usually quite pleased to be asked to help!
Weather permitting, we get out for lots of walks. Usually stopping at the park so the older one can play on the swings.
I remember crying when my husband was going back to work after his 2 weeks paternity leave wondering how on earth I'd manage on my own. It does take some time to get into your own routine, but you'll get there, and you'll wonder how on earth you found it hard with just one!
I did find pregnancy a lot harder second time round, am very glad to not be pregnant any more.
Congratulations! It's lots of fun having 2 close together.