The accurate answer is Danault. As much as I'm not a fan of his comments at the end of the season and as much as I think it would be stupid to pay him north of 5.5M on the long term, the focus should be on grooming Suzuki and Kotkaniemi to be the driving forces of our first two lines. And to do so, you want to have a veteran who can handle some tougher matchups.
Ideally next season Kotkaniemi gets mainly exploitation matchups, while Danault and Suzuki split up the tougher assignments.
Play Suzuki with Drouin and Gallagher. Kotkaniemi should play with Armia and an offensive winger we acquire this summer. Danault, Tatar and Lehkonen can play some tougher minutes here and there.
One guy I'd try and get is Granlund. Finns have great chemestry together, Granlund would be cheaper after a tough season. He's still young. And even if he's small he would have tons of room to manoeuvre with Armia and Kotkaniemi.
As for Domi, I think I would actually do a one on one for Nikita Zadorov if Colorado is interested. Chiarot, Weber, Zadorov, Petry and Romanov on the same D is probably the most intimidating D in the league. And every single one of these guys are decent skaters for their size.