After coming from a four string, the one thing most people don't bring up (after moaning about finding the perfect B-string, their old amp ain't up to this, the fingerboard's too wide/narrow, etc.) is this mostly left-hand problem of the 'extra' string(s) ringing until you learn to mute them effectively as part of your now-expanding technique.
This is why the 'classic' neck taper was good for me: The string spacing was close and the neck wasn't very wide. I live close to a SamAsh store who's had a John Pattitucci Yamaha in stock for a very long time. Aside from the awful pickups, I'm convinced it's because it's the widest fingerboard I've ever tried, and I have big hands.
I use a variation on what you do: I tend to rest my thumb BETWEEN the E and B, the A and E, etc., instead of upon a string singly. I had to learn to pluck more across than 'into' the strings, as well. I come from a piano background, so the idea of lifting out of each stroke is ingrained, as well as not letting anything keep 'ringing' that's not part of the passage at hand.
I hope this is useful.
J o e y