I have a slightly smaller gap than you, 15 months, and I bf my eldest for 10 months stopping as the second pregnancy got further along.
DD1 wasn't at all jealous about DD2 coming along though she was very, very interested in what was going on with my boobs. She started breastfeeding her teddy whenever I fed the baby though she would get upset because she was in the popper-under-the-bum vests so couldn't pull up her t-shirt like I could. I had to explain that teddy was special and could feed through her t-shirt. It was very cute but some people didn't know where to look when they visited with me feeding baby on one sofa and DD1 'feeding' teddy on the other sofa!
I let her come and have a good nosey at what the baby was doing, let her touch and explained that the baby was having 'mummy milk' just like she used to have. She was very interested but never wanted to bf herself. By then though, at 15 months it was 5 months since she had been bf and I doubt she could really remember that she did.
After I had bf the baby I would make sure I had some cuddle time with DD1 so that she didn't feel she was losing out on physical contact with me because of the baby. We got a lot of library books out each week and we would read one together 'to the baby' so that she felt like she was being helpful and doing something for DD2, though DD2 was usually asleep of course.
I prerecorded DD1s favourite cbeebies programmes and I put one on sometimes when I started a bf to give myself 10-20 minutes when DD1 would be entertained with something else. I also bought lots of little, cheap presents for her. Second hand books, little cars, pretend phones - anything small and cheap. I wrapped them up and if she was driving me mad whilst the baby wanted feeding/changing and I just needed 5 minutes to get sorted I'd give her one. it took her ages to unwrap them (I used lots of sellotape
) and then spent a good 5 minutes+ playing with it.