GOOD THREAD!
OP, tell me what you think about this: When I had my Boston Terrier, which was about 15/16 pounds at most, we had a big, rectangular cardboard box (w/ tall sides) right outside the back door in the garage lined w/ some layers of newspapers that one of my parents or myself would literally carry him to go & we lived in a 2-story house. We'd just take him every few hrs. (We never had any grass either.)
We kind of trained him from an early age to know the word BATHROOM, so when we said it, he went. We didn't wrap up & throw out the top layer of newspaper every single time though because it didn't get dirty that fast & wasn't really stinky. When I moved to my 2nd floor apt, I put a cardboard box out on my outdoor patio balcony & did the same method.
Would I do this method again w/ a future dog? Maybe, but I'd love to see other suggestions too.
Anything I'd do differently? I'd try to train from day 1 to ring a bell so they could let you know when they have to go but I don't know how easy that kind of training would be. They've sold these for a long time now that you hang from the doorknob:
https://www.amazon.com/CandyHome-Doo.../dp/B01DDIV18K