Reddit mentions of Ballroom Dancing, 10th Edition

Depends on the size of the space, but you can usually practice fundamentals like driving, balance, etc. in a small space. Waltz is a good vehicle for practicing all of these; try doing a single half natural/half reverse or change step and then reset. To train your balance, do a half natural/reverse slower than normal and make sure that you lower at the 'and' of count 3. If it's too easy to stay balanced, try turning down the tempo.

If you follow (and even if you don't), heel turns are also a good thing to practice, and they can be practiced in a small space.

If you are doing standard, I also recommend a copy of either The Ballroom Technique, Ballroom Dancing, or both. These are by the same author and have roughly the same content, but the first is more of a quick reference (and does not include a section on V.Waltz). You can also look up the same content on Ballroom Guide's workshop page for free.