Elvis, your HV is talking crap, sadly.
If your baby seems to want feeding on and off in the evening, this does not mean a low supply...in a baby who is otherwise doing fine, it just means he is what's known as 'cluster feeding' and it is very, very common. Eating, drinking and rest will make no difference - their role in milk supply is grossly overstated.
One way of managing it is just to feed him, if that's what keeps him happy. Of course if you have other children it is about the worst time of day for just chillin' on the sofa with baby, and you need to work out a modus operandi, maybe involving partner, different routines for the older kids, a sling so you can do other things while the baby helps himself.
Feeding him not only gives him what he wants, it maintains your supply in line with his needs.
With an established milk supply, one bottle may (I say 'may' not interfere with supply, but you need to factor in the hassle factor of it...someone has to make up the bottle, sterilise the teat and bottle, cool the milk (and then warm it up, though this is prob not necessary), and sit and feed him. You might say this would free you to bath/feed the older kids....but someone else can do that while you breastfeed