Lane if you def want to stay with ebfing then DO NOT give a formula top-up. You can up supply/improve quantity of milk/increase weight gain in a number of ways. You can block feed (same boob for a number of feeds or hours depending how you feel - this increases hind milk baby gets), express fore milk off before a feed, feed more regularly, use breast compression, try supplements and diet changes, to name a few. I'm not anti-formula if that's what you choose to do, but its a lazy suggestion by HV etc to improve weight without understanding it actually decreases milk supply & results in the early cessation of BFing.
Rather typically, I get our dinner on the table & junior wants feeding!! I'm sat with him on the tit, with a cushion on my lap, spooning pasta into my gob. Girl's gotta eat!!!
I've tried to get junior weighed 3 times in the last week (he's 23do & last weighed at 12do) and failed - the first time because I was running late & couldn't DP the clinic AND his tongue tie feeding specialist appt, but the other 2, because the clinics were cancelled.
I will get on the scales at home later...
Junior seems to sleep lots so hasn't really shown many preferences but he likes his playmat & his big sister!! :)
Still not sure if our family is complete. Head says "all done" heart says "maybe...??".
Thought the whole "you'll spoil them" thing went out of fashion in the 70s. My Mum kept being told that because she BF me, kept me by her bed in the hospital (didn't have me put in the nursery & take a sleeping pill
) and picked me up when I cried. Ahead of her time clearly 
Oh and horsey I felt the same - couldn't imagine having the time or head-space for more than one, then suddenly I became really broody. If you only want 1, nothing wrong with that, but you may find your hormones get the better of you. For some (like YW & a couple of my RL friends) can contemplate it straight away, but it took me about 18mths before I wanted that.