Thank you everyone who has offered their advice and experiences - too many people to reply to individually.
What I would say is that I absolutely understand my partner has been through a lot; I'm actually amazed what mothers go through - 9 months of pregnancy with nausea, giving up foods (she's French so loves unpasteurised butter and cheese, wine, coffee), the discomfort of carrying the weight. Then birth which for her was full on as she went into active birth off the back of 48hrs of no sleep due to a long latent birth stage. Then after birth, there's the recovery whilst looking after a baby.
Funnily enough, before he was born, she did openly discuss it might be difficult to adjust from him being in the womb, just her and him - to then being out there and he's more than just hers (not sure if I'm explaining this well). Which I absolutely understand, although being male, couldn't possibly truly understand.
@fez - You're completely right about the access to information, honestly, you watch these YouTube videos about different holds and stretches as if they're guaranteed solutions. What doesn't help is she's either proactively using AI or getting the AI summary when searching, where AI can often reinforce your belief depending on how you've asked the question. For example, he's been on infacol and gaviscon infant and she's leaning to giving him neither because she's seen gaviscon can cause constipation (I can't even remember the infacol side effect she found). There's a lot of knee jerk panic buying, including a humidifier as he had a couple of nose bleeds and now it's not used because she felt the mist coming out has changed, suggesting it's probably limescale but we've been using distilled water with it. I don't mind, it was £25 (I think) so not a massive waste of money but gives a view of the mindset.
Her mother was with us for ~3/4 weeks after he was born, she wanted to be around as her other grand children were born in Canada so couldn't be around for their birth. My partner a few weeks ago mentioned she felt she was taking frustration out on me now as previously, it was her Mum taking the brunt of it, I was just unaware as the conversation would have been in French.
It's all good, I think there's a level of acceptance that she's going to need an outlet of her frustrations, especially considering she's still going through postpartum recovery, breast feeding, having him for 80% of the time he's awake.
The main challenge for me now is understanding if his behaviour is normal or not, which is a challenge in itself not having any experience to go on. The two things that concern me is his feeding, regardless if he's at the breast, or at the bottle with expressed milk, he sounds like he's never been fed. Gulping, gasping, snorting, kicking off if you remove the bottle after giving him half to burp him. I then wonder if the feeding behaviour is linked to the other issue, which is outside of feeding, he's generally just fussy/crying - it either sounds like he's pushing wind or stool, or it's fussiness just before bringing up milk. He doesn't sleep much during the day, if he does sleep it'll be for 30 to 45 mins, max twice a day, before waking up in clear discomfort but does do 5 to 6 hours overnight.
We're on either size 0 or 1 teats for MAM bottles to try and slow the rate of feeding down.