100 buy-ins seems WAY too conservative and it's probably a good safety net for degens with absolutely no self-control.
If you are consistently profitable at your current level and you want to take a shot at the next level, I would say 30-40 buy-ins are more than enough, as long as you have a reasonable stop-loss and respect it. Let's say 5 buy-ins downswing.
The thing is, you must be honest to yourself. Are you really winning at your level or just running good? Are you willing to step back as soon as you reach your stop-loss? Some people have no self-control and for some reason see stepping down as a major defeat, refusing to do it.
Example. This is my 5NL graph (I have a goal of 50k hands before moving up).
See the downswing from hand 10k to hand 16k? That's 15 buy-ins. So it would be half my bankroll if I was taking shots with 30 buy-ins. It would be 15% of my bankroll if I was taking shots with 100 buy-ins.
The thing is, it started with this single session:
6 buy-ins in 1000 hands, but the EV line is break-even. Let's say this is my first session taking a shot at a higher level. I lose 6 buy-ins in a session in which I ran like literal ****, so I blame it all on bad luck and keep playing.
A couple days and half my bankroll is gone.
So if you are disciplined and step back to your comfortable level
right after this initial losing session, you can take your shot with 30 or even 20 buy-ins.
If you aren't confident enough in your sense of discipline, then you need a bigger bankroll.