I can't speak for boxing but as someone who does weight lifting, you can get pretty far by just lifting at home (and go to the gym for heavier weights or start purchasing more expensive equipment if you have the space for it)
Julian from HN has a great guide on how to do this, I always give him a shout out when I can because his guide is very sensible and easy to follow:
https://www.julian.com/guide/muscle/intro
I think the most important factor is consistency and discipline. It's more of a lifestyle change than achieving a certain goal and you have to be patient with yourself. The rest of it pretty much boils down to: sleep, eat enough calories and lift a bit heavier every time..
I love Bowflow adjustable dumbbells. You can go with 552 or 1090 depending on how much experience you already have and how strong you are: https://www.bowflex.ca/en-ca/selecttech/552/100131.html https://www.bowflex.ca/en-ca/selecttech/1090/710000.html
Julian from HN has a great guide on how to do this, I always give him a shout out when I can because his guide is very sensible and easy to follow: https://www.julian.com/guide/muscle/intro
See the relevant thread: https://news.ycombinator.com/item?id=12618223 .
I think the most important factor is consistency and discipline. It's more of a lifestyle change than achieving a certain goal and you have to be patient with yourself. The rest of it pretty much boils down to: sleep, eat enough calories and lift a bit heavier every time..
Good luck!