I had an 18 month gap with ds1 and DD, and 2 years between DD and ds2.
It was very hard as they were all terrible sleepers and I felt so tired until ds2 slept through.
I found routines really helped, I went to toddler group twice a week and song time at the library, and went to the park or soft play on the other days, money permitting.
Ds1 loved having a baby too, and he would help fetch nappies and play with toys. I remember he watched Timmy Time lots as it lasted as long as DD took to bf and he would sit beside me and have a cuddle.
Try to have a bumbo or baby chair in every room, or ones you can carry, as you never seem to have enough hands to deal with the toddler when holding the baby (although I once arranged a gas supply transfer over the phone, writing things down and bf'ing DS at the same time, I was most impressed with myself!)
Be kind to yourself, my dc are very close now as they were so close in age, but I wish I had been less uptight when they were tiny and enjoyed it more. It's easier said than done but I wish you luck, it was all worth it.
I worried so much that I couldn't love DD as much as DS, and when she was born, he said 'baby' and kissed her straight away, and I realised how easy it was going to be to love her, even a child could do it.