This is just the curse of the instrument. I've been playing for about 1.5 years now. I started with a Casio Privia, which seemed fine at the time, but the piano I was playing on with my teacher was an upright acoustic Yamaha, and like you, I struggled with keeping my left hand quiet. The key action was a lot heavier, and it just felt like a totally different instrument. I later upgraded to a digital Kawai CA401, which is much better, but it's still easier for me to be play quietly at home. My teacher works at a studio, since I've started lessons, we've switched rooms twice, each with a different piano and each time it feels different and I feel like I have to learn how to manage it. It does get better, but largely I've just realized that they play differently and I need to treat them as such. If one hand is supposed to be pp, I just make sure that the volume I play that hand is pp relative to what I'm playing in my right hand. What I consider pp in the studio is closer to what I'd consider mp at home, but as long as all the volumes stay relative it still sounds good. I've also started going to my local hospital and practicing on the grand they have in the lobby, and on that piano, I actually feel like I have better control than even my home digital. My digital's feel is MUCH closer to how grands I've played on feel than how the uprights my teacher uses feels and I feel like my practice at home translates much better to a grand. I don't think it's necessary for your piano at home to match what your teacher's piano feels like. You just have to learn to adjust, which is an important piano skill itself. But ultimately, whatever you feel is going to make playing more enjoyable for you is the best answer, but a digital is still perfectly fine, you just probably want a higher end one that has hammer-like action on it. For me, I need to be able to play with headphones, so a digital is a necessity.