Yes, to save space getting an in-wall tank system would be best.
Yes, the in-wall tank and carrier model number is 111335005. There are two options on the seat, model 0069890000 is a SoftClose seat and model 0069810000 does not have the SoftClose feature. You would also need a dual flush actuator which is model 115770111 but there are other options on the actuator.