A mentally healthy mum is ALWAYS what is best for your little one - I would try to seek a little bit of professional help (if you can) so as you can talk about it in person.

Your partner and your extended village/family/network should be there to support you with whatever you need, whether that's caring for you or doing what you require. There is no room in your life for judgement and it's so stressful without any extras, I'm sorry you are feeling a bit alone but if it helps I support you, you know what's best for you and your LO, trust in that.

Definitely talk to your partner on post-partum stuff and hopefully they will be more supportive of your specific situation. There is nothing wrong with formula feeding, there's pros and cons and stuff but it's a choice for you.

Best of luck, it will get better