MSG + the egg-white technique were two of the best upgrades I did after learning the sous-vide process! Shiitake (more umami) & porcini powder (less umami) are also pretty awesome if you don't mind investing ten bucks into some powder off Amazon (or locally, if you can find it!), but I'd say start out with MSG first & get to know how much to use, how it supplements the flavor in various meats & vegetables, etc.
Trader Joe's has a nice mix called Multi-purpose Umami Seasoning Blend if you want to try something off-the-shelf first, it's pretty decent for a pre-blended mix:
As far as the egg-white technique goes, read up more here:
If you're interested in picking up some new kitchen toys, I highly recommend the Evo sprayers: (they can atomize oils into a spray! sort of like all-natural Pam, without propellant as an ingredient!)
They come as a pair, which you can use for EVOO, canola, water, apple cider vinegar, etc. I always keep one full of canola oil to coat pans, meat, etc. You'll want to get one if you plan on using the egg white powder (as opposed to pasteurized liquid egg whites, which you can either buy in a box, or buy pasteurized eggs, or just pasteurize the eggs yourself in your sous-vide setup at 135F for 75 minutes followed by an ice-bath shock).
It's pretty fun because umami exploration adds a new dimension to cooking & lets you see what you personally like, what works & what doesn't flavor-wise, ratio-wise, etc. And it doesn't just stop at MSG...there's mushroom stuff, soy stuff, koji stuff, fish sauce stuff, etc. to play with! My Instant Pot chili uses both fish sauce & Worcestershire sauce & comes out pretty amazing!