You can't change what has already been done, only what happens now, so no point in beating yourself up about it. Very, very hard for you when you are even getting pressure from your husband about it.
https://www.kellymom.com/bf/criticism.html
I was reading this today about criticism of breast feeding and it might be helpful to you? There is also a link about BF facts that might help? One thing I did find interesting is where it says that
"Sometimes the people close to you - particularly your parents - feel that when you make parenting choices that are different from their own, it is a personal attack on their own parenting choices. They may truly feel that accepting your parenting choices is the same thing as admitting that their own parenting choices were wrong. It may be helpful to make it clear that your choices are not a judgment on their parenting, but a result of having different information available that you are using to make choices for your own unique child and family"
which is maybe relevant to your particular situation?
You are absolutely right about this, so don't let others undermine your confidence, but I appreciate that it is very hard when there is pressure and questioning from all sides.
I am lucky in that no-one questions my choices as I'm a bolshy cow who would give them short shrift and they know that, but if people comment about my daughter feeding a lot, for a long time or feeding at night I just reply that 'babies/evolution are very clever and babies feed a lot and wake at night specifically because it gets your milk supply up and keeps it up to a level the baby needs, so it's a good thing that my baby does this'. Then I give them what my husband calls the 'wife smile'
and they shut up.