I've enjoyed some soft 'n hefty mids in recent years for singles slugging with an extra significant component of control, but I don't hit a whole lot of strokes in doubles. More of my shots are "punched" around the court as I'm always looking to press the net. A soft, stable frame is okay for this sort of play, but I'm much more confident with a livelier alternative.
I grew up playing serve & volley and for many years I've had a great time with my ProStaff 6.1 Classics. While they're hefty and rather stiff with some healthy pop which is great for me around the net, they're also a bit hot in a singles setting where I need to produce more consistent strokes. A more flexible alternative like the Volkl C10 Pro or my Prince NXG's (mid or midplus) makes all-court play with extra baseline action much more manageable for me.
While a K90 could be potentially great for your doubles, another frame with enough stability, decent handling, and good pop could allow you to be quicker and snappier, especially around the net. Trouble is, you only know if it's right or wrong when you feel it (hello confidence).
Something from the different 6.1 95 models that Wilson has produced could be worth a try. Others possibles could include the Prince Ignite 95 (sort of their version of the 6.1's), a current Yonex like the RDiS 100 mid-plus (or even the mid!), or who knows what else. For my tastes, a good doubles option needs enough weight to feel inherently stable, enough HL balance to have good maneuverability, and enough backbone (not too flexible) so that my blocked returns of serve and my volleys have enough zip and authority.
You may actually have no need for a separate doubles specific racquet, but you'll probably only have a better sense of that once you've done your own "Pepsi Challenge". If you can do a little trial and error, you may find something useful, but the process might even reinforce the confidence you have with your current gear.