I’ll be honest, I would focus more on what feels right for you and your DP, rather than your DS - if it feels right for both of you, it will be easier to manage his feelings. If you feel ready, go for it. If not, wait. If you had a difficult pregnancy or might be planning a c section, it may be preferable to wait until DC1 is a little more independent but not necessarily if you have family support.
We have a 4.5 year age gap. I thought it was going to be great - DC1 nicely settled in school so lots of time with DC2 at home and doing baby groups, no double whammy of childcare, etc. Covid hit wen DC2 was 8 weeks old. Short version: I wouldn’t plan if I were you.😂
Advantages for us are that DC1 was more independent and I had more time with DC2, Covid notwithstanding, in a way that wouldn’t have been possible with a smaller gap. We didn’t have to rush DC1 out of a cot or car seat to accommodate DC2, or buy two of everything. No double childcare costs.
Disadvantages are that the age gap can mean they have very different interests and won’t necessarily play together. In our case they are the same sex and DC2 is very interested in DC1’s toys, which isn’t ideal either! We also had just got to the stage of life being easier, not needing a buggy and a tonne of stuff to leave the house, etc, and then were suddenly back to square one. By the time DC2 starts school, I’ll have spent 9 years parenting preschoolers!
A number of friends of mine have much smaller age gaps, including as tight as 18 months, and they are generally very positive about them. It looks crazy for me but what I did notice was that suddenly, life seemed to get a lot easier, a lot faster, for those friends - a couple of years of crazy chaos and then bam, DC2 is starting school, careers getting back on track, and all looks good.
Everything has its advantages. Go with what you feel is right for you.