Jealousy

So me and my husband are trying to decide when the right time is to start trying for another baby. Our daughter is currently 8 months but I wanted to be done by now and we just got started. I don’t mind my kids being close in age but what concerns me is the jealousy, what are everyone’s thoughts on jealousy as far as the older sibling...I mean obviously I think the older they are the more they understand that things are different and not as much attention is on them anymore...but do children realize that even at 1-18 months, I feel like 1-2yrs old kids wouldn’t be as aware of not getting at much attention, I’m not sure if my thoughts are right but would love to hear from some people who have children close in age and some people who don’t, what were your experiences as far as the older child being jealous of the new baby? Thanks!