> If he's gaining well then his restlessness could be because he is taking too much being a singleton, or he's simply a crosspatch and impatient.
Agreed. Some puppies are just 'fussy' when nursing. If he's a singleton, it would be VERY unlikely he's not getting enough from mum unless for some reason, she isn't producing milk at all. We had a couple of singleton 'litters' and if anything, had to be careful to rotate the puppy round all the teats, or risk mum developing mastitis. I don't see why you should need to be supplementing him at all, provided he is gaining. The act of nursing should promote lactation so provided he's otherwise okay, and gaining, the more you can leave him on her, the better. Is she attending to his emptying because some of this could be simply he's uncomfortable!!
ps The first time we had a singleton, I panicked because mum was hardly eating at all. I didn't realise why - nature dictated that she only had one to cater for, so she didn't need much food, and fact is if she was eating as expected, she would have been making more milk than he needed.