Under pressure from HV - do you think this is an acceptable weight gain?

[Liv77]

I'm after your opinions DC2 will be 4 weeks old on Thursday. She was 6lbs 1oz when born at 39weeks+4. Last week she was 6lbs 4 and today weighted in at 6lb 6oz.

HV wants me to top up feed with 4oz 3 times a day, I wouldn't be able to express that much and usually only get a couple of oz expressing so would have to use FF.

DC1 also had to be mix fed due to bad reflux and a similar slow weight gain not helped by tongue tie (where I live don't operate for TT unless it affects their speech in later years) DC2 has also got TT. I had really hoped to be able to exclusively BF this time. (It is the same HV I had with DC1, who advised top up feeds for him)
DC2 seems fine and pretty content to me, although her weight gain is slow. HV thinks that she seems content because she is exhausted from inefficient feeding so falls asleep but she is often awake and not always crying and feeds on average every 3 hours. Often when she falls asleep at the breast I take her off and she has a mouthful of milk, if she wakes i'll offer her the other breast.

What do you think, should I give it another week and see how she goes? I've only expressed a couple of times so far so I'm going to increase my attempts to a couple of times a day.

Am i being a bad mother if I ignore the HV and don't top up my BF with formula or is my HV just being overly cautious, she didn't tell me what an acceptable weight gain would be.
Your advice please

thanks for all your responses.
i have given dd a couple of top ups of formula over the last few days, it's now settled into 1 top up every 12 hours. one late morning and one late evening She'll generally take 2-3oz formula from a 4oz bottle and has lost no interest in the breast.
I had a half duvet day (my 3yo was missing me so i had to get up for lunch) but i was already putting dd to the breast whenever she cried, was rooting or if she hadn;t fed for a couple of hours and dh/my mum were helping at home and with my ds when they could so i could rest and feed dd.

Although i said in my original post she was feeding 3 hourly, that was overnight. The daytime feeds last for hours (they still do) and i was feeding pretty constantly so TBH i couldn't really increase the time spent BF.

Anyway i took dd to be weighed today (at the clinic my HV doesn't do ) and the result is she has gained 10oz in 7 days and is now 7lbs so slap bang back on 2nd centile line.

Again thank you so much for all your support and advice, it's been greatly appreciated