In the film era, I used Nikons, Hasselblad, Mamiya 7, and 4x5. In the digital era I used Nikon, Olympus, and now Fuji. As others have said there is a different workflow with mirrorless, a more efficient, easier, more pleasant workflow in my view. I also agree you should rent or borrow a mirrorless camera for long enough to understand and appreciate these differences. The entire concept of exposure in mirrorless is simplified, you see, you get, and with a current histogram in the finder if you wish, without a loupe on the back of the camera in clumsy live view. It's always live view, with lots of information... or none at all, depending on your style. The difference is almost as profound as digital vs darkroom printing. In darkroom printing you iterate with lots of sheets of paper guessing each time if this print will be "the one." In digital printing, with a calibrated system, you get it right on the monitor and often get it right or very close with the first print. I enjoy using my lighter easier to carry about mirrorless camera a lot. You may or may not. Be aware that while the M4/3 and Fuji systems have many small excellent lightweight lenses, the full frame mirrorless, e.g. Sony, require larger often heavier lenses to be fast and cover the full frame sensor. There are smaller primes in the Sony system but the best zooms are pretty big. That may or may not be a deal breaker for you. I put together a spreadsheet with the weights of the bodies and common lenses for Fuji and Sony. PM me if you'd like to look at it. Try not to fall into the trap of thinking you'll realistically use your "legacy" lenses just because you can mount them. Most do not work as well and significantly complicate things except of certain exotics (I kept my Nikon tilt shift lenses).
Good luck on your quest. Ask the hard questions, what do I gain, what do I lose, is it worth the money? But have fun.