I don't think you'll find a book but make a thread asking for tips from other mums with a small age gap and you'll get lots of replies.
I've got a 16mo age gap and I've found people so, so helpful as we all know how hard it can be.
There's a '2 under 2 UK only' group on Facebook that's very active. Sometimes it's just people having a vent but you also get some good advice on there.
You need to be super organised. Start making a list now of all the stay & plays in your area something for everyday of the week. Only do drop ins - don't bother with anything you have to book termly as that turns in to a stress trying to make it. Holy grail is safe space for older child to play without your input with tea and biscuits available (at least).
Follow older child's routine, DC2 just have to slot in as best they can.
Get a baby carrier for the first 3 mo and then explore a double buggy.
Cook a dinner that can be lunch tomorrow as often as humanly possible.
Eat out whenever you can, avoiding cooking and mess.
Rotate your toys. Only getting a few out at a time. Avoiding a big clean up and keeping the interest fresh.
Think now about how you are going to approach DC1's nap time. How will you put him down if baby is awake? Will he nap in the pram or the car?
Can you make sure that baby is asleep before you need to be DC1 down? Which would mean waking baby up at the same time everyday so you can actually plan wake windows and nap time to line up with what you need.
I could go on and on...
I reckon it's easier the smaller the gap!!