Hi Laura, our age gap was slightly larger at 2y5m but things we did were lots of talking about babies, what they eat, what they might be trying to say when they were crying (I'm tired, I'm hungry, I need a nappy change) etc. We read a princess polly book which was quite good - I think it was this one
https://www.amazon.co.uk/Im-New-Big-Sister-Princess/dp/1409313735 And we also did a few practical things like moving DD out of the cot bed into a big bed so we could put the cot bed away for a while before baby arrived, so DD didn't feel like baby was taking her things.
There will always be an adjustment period but I think cuddles and reassurance go a long way. Involving your DD as much as you can might help too - get her to choose which clothes or nappy baby wears or help pass you wipes. Keeping the older one in routine was a must here - really helped DD realise that things hadn't changed that much and I think made her feel secure.
The other thing I would just leave with you to think about is just being conscious of not always prioritising the baby - by that I mean obviously baby's basic needs absolutely have to be met, but I found that consciously choosing sometimes to have a day out somewhere or spend time on an activity because it was what DD needed really helped us. The baby's needs are initially very practical, but your older one will have emotional needs also which are just as/potentially more important to address. Baby can cope with a day of rubbish naps now and again!
Good luck, I hope the rest of your pregnancy and delivery go smoothly x