Thinking of baby #2

So my son will be 3 months this Friday and yes God help me I'm thinking of baby #2 I turned 24 in August and was actually thinking of start trying my birthday next year. My partner has 1 from a previous relationship so this will be his 3rd not sure how he will react seeing our son will be 1 in June and 2 months later I want a baby. This will be the last one I would want so I kinda want them close-ish in age. So I guess long story short any tips on how to get him on board or am I crazy?