My knee jerk reaction is to want an upgrade on Aho and Bolduc. So in looking around at guys who might be available, and who would provide some puck-moving ability to pair up with Mayfield, I saw Brannstrom and Boqvist and thought either would be great. Digging down a bit more though, I'm not sure either of them would be an upgrade on Aho, and they have cap hits of $2M and $2.6M (Aho is $800K). And yeah, Aho gets beat physically, but he's the only one of the Isles' 7 D who isn't big (and virtually every team has a smaller D or two).
Re: Bolduc, we have to remember that he's 22 years old and is a big (6'4", 220lb) defenseman - the guys who traditionally have the longest development curve. So with just 17 NHL games, maybe the smart move is to live through some growing pains and allow him to develop. Similarly, even though Aho is 27 he has only 133 NHL games (for comparison, Romanov has 210 NHL games and Dobson has 239). So maybe the plan is to let them get in games this year, and if at the TDL they feel they need a vet they can make that happen.