If your current keyboard is weighted I would stick with that until it breaks. For me, PC's or Mac Garage Band sounds better/as good as any digital sounds built in to a keyboard. So I ignore built in sounds which are not upgradable, and go entirely on touch, which is great, as you can evaluate without plugging in. Sounds like your idea. Lots are acceptable, almost all Rolands and Yamaha Clarinova's. In practise I buy any weighted keyboard for less than £300 off ebay. Pedals & stands are expensive separately (watch out), and you might get a nice stool thrown in.
I tried Yamaha acoustic upright pianos in silent mode also. They have Midi out, and hold their value better than a pure digital only piano. The best for feel, better than the acoustic in silent mode, was a Roland HPi 7F with a PHA III keyboard, which really does feel like a baby grand, great touch. Sounds were unconvincing, and it is overly large, heavy, perhaps just over your limit, but there may be a cheaper model with that keyboard. I also tried the Yamaha Avant-Grand, a new one in for Christmas. It didn't feel like a proper grand, but was better than a normal digital. The Roland possibly felt nicer than a low end grand action. After I pressed a key on the Roland, it felt like the hammer was hitting a string. On the Avant Grand that sensation was missing.
I have been thinking about getting an old grand piano to put in a silent system, as I don't want my curent acoustic messed with. Could be a lot cheaper that a high end digital, and the pedal weight and case rigidity of the piano never feel right on any digital I have tried.