Johnson would be a pretty good fit IMO as well.
He's learned to reign himself in and isn't always going for the big hit anymore à la Phaneuf. If they limit his role this year to Bartkowski's minutes, they can't really go wrong - 4 years at $4.4m left after this season is pretty good to have him in his prime years as well.
When Seidenberg gets back they'd be looking at a Chara/Seidenberg/Johnson/Hamilton top-4 (assuming Boychuk would have to go for cap purposes).
Question is the cost, as always. If there'd be a deal to cash Khokhlachev in on, alongside someone like Morrow, JJ may be it. Would be nice to get out of it without much more than that but picks aplenty would likely have to go to save Subban/Spooner.