^^^ This. I use a simple (and free) metronome app on my smart phone. At the beginning of each practice session, I set the tempo to a certain BPM, and play 16th notes at that tempo for a couple minutes on each string - straight through with no resting. Then I bump up the tempo and do it again, and again, and again.Regularly practicing with a click or drumbeat, and gradually increasing the tempo until you can play comfortably and steadily at higher speeds, is the only way I know to get good at it.
Three finger plucking is something that depends a lot on the player. you can develop the ability with practice. But for most of the players I’ve known over the years, three and four finger plucking either comes naturally or it doesn’t come at all. I can pluck with three fingers when I need to because I worked at it. But it’s not something I could ever make feel completely comfortable for my hand. Best bet is give it a try after you get your two finger technique up to where you want it. You can never know too many techniques IMO. But it’s best to only focus on developing one technique at a time.
The cure for floppy strings is to either try a different string set that has higher tension -or- play with a lighter touch. As was previously suggested by @Lobster11, the “floating thumb” technique almost forces you to play with a lighter touch. So that may be worth trying before you start switching strings.
Luck!![]()
I actually never developed a full floating technique, other than shifting my thumb anchor from the E to A string (and back) to play notes on the first two strings. And I only do this if I'm playing an extended series of notes on the first two strings. But then again, I only play 4 strings and I have big hands, so it's not so hard to play by anchoring.