Ferber tends to work quickly if it's going to work, apparently. If I was going to try it then I'd set a time limit and abandon if it's not working. I wouldn't keep going for weeks and weeks with no success, nor leave them crying for hours. I think it is a good idea to set your own tolerance level for this before you start, rather than going in with a mindset of "whatever it takes" (unless you are genuinely OK with that).
If you wanted another option, what I found with my DC is that once I moved them into their rooms and stuck to my plan of resettling them in their own room, they stopped waking as often. There was no leaving them crying with this method, but it did take longer than a crying type method - as in weeks, not nights, and was more disruptive to my sleep because I was going in and out of their room and staying there through failed resettles, which is frustrating. If you start this and are struggling to stick with this, then you can set yourself little "stretch goals" like - I'll try to keep them in their own room until midnight but any waks ups after midnight they can come through and then extend this to 1am, 2am, 3am etc. But the more consistent you are the quicker it works.
My DC were also older so I can't promise that it will work for a 7 month old but in theory, hopefully it might reduce wakes even if not eliminate them entirely.
It depends what you're willing to prioritise really - I don't think sleep training is totally benign, especially if it's causing extended distress for multiple nights in a row, but OTOH I don't believe that it's so incredibly harmful that it's going to cause permanent damage within the context of an otherwise responsive relationship - that's just not how relationships or brains work.
There are other situations where we opt for short term distress in order to achieve a longer term outcome, and I don't think sleep is magically different. OTOH you would respond to DC in the day, and night is not magically different. But in the daytime, we do sometimes place limits on how we respond to DC too - for example, if they are crying in the car seat, we don't take them out because we know that it is needed for safety. Or if they were crying for some dangerous thing, we might comfort them and offer them an alternative thing, but we wouldn't let them have the dangerous item.
People get really polarised about sleep and I think it's unhelpful.