Oh this old paradigm.
I'm childfree by choice. I have read numerous books, research papers, articles etc.
A big theme that comes out is parents in your position who have one child and the ridiculous pressure put on you. This is the reason for your guilt - external pressure.
In the book The Baby Matrix, Laura Carroll scientifically debunks ALL of the obnoxious things you get told as a parent of 1 child.
Only children are more likely to be successful in later life.
Children do not need siblings to develop social skills.
I had too many siblings and it caused no end of issues.
Please please try and work on that guilt. This is a decision for you and your partner to make alone. Society has no role in even commenting.
Our sociaty is extremely pronatalist. This means it automatically and absentmindedly pedals reproduction. The comments that you receive are not personal, they are through robotic mouths.
Let's be honest, if you had a 2nd and it was a girl, people would push for you to "try for a boy"
You got this Megan. Look into your own soul and go with whatever YOU want.