Indoor cycling bike options

First of all forgive my English, I don’t know if I can express myself accurately.
I already have a giant rim brake version of tcr road bike, I ride Monday to Friday for exercise at my work place, Saturday and Sunday I will go back to another city, more than 100km away from each other, I would love to buy another bike to connect to the riding platform for training, I have already purchased the new riding platform, but I don’t know how to choose for the second bike. Is it a good idea to buy the disc brake version of the bike, also, I might train at home on weekends just training the z2 and maybe riding around for an hour as well, as I need to take care of my family, I might not get out on the bike a lot, mostly indoors I guess.
I am now thinking of buying a Canon Dell aluminum frame road bike, preferably an endurance frame for more comfort, after all, my wife does work out. I haven’t tried a mountain bike, maybe a mountain bike is a better solution? after all, indoors you need to z2 for long periods of time, and the mountain bike position might be more comfortable.
I really have no experience in this area, so I hope you can help me, thank you very much!

I bought a $100 road bike to keep permanently on my indoor trainer. I love the setup. Just get in and ride. The bike doesn’t need a rear wheel or brakes. I always use ERG mode so shift quality doesn’t matter either.

Smooth shifting is still pretty important because TRAINERROAD can sometimes go into a death loop, especially on high intermittent courses. BTW, have you purchased the lockout pedals yet?