To do what you want, you must either go with prime lens(es) or else one of the heavy expensive zooms. I use the 24-70L (it's f/2.8, BTW, not f/2) most of the time, but occasionally the 100/2 or 135/2L primes. When it comes to shooting in low light, there are no shortcuts. You either must have fast, heavy, and expensive glass, a body that can deliver low noise at high ISO, or both. There are no shortcuts or cheap magic bullets. Primes are lighter and less expensive than zooms, but you need to have the freedom to "foot zoom" in order to use them. In many situations, you don't have that freedom for one reason or another (room size, furniture arrangement, being limited to a certain area, etc.) and a fast zoom is your only choice.
The weight and cost of fast lenses is directly proportional to aperture size; an f/2.8 aperture demands a larger, heavier lens than f/4. It's basic physics. If weight is an issue, start hitting the gym a bit more often. As to cost, if you aren't getting enough of a financial return from the project to financially justify the purchase of the proper tools for the job, don't waste your time with it. You certainly aren't doing yourself any favors if you do, and you're devaluing photography as a profession and making it harder for working pros to make a living.
Ollivr, doing head & shoulder shots with a 30mm lens, even on a 1.6x body, is a really stupid idea unless you want the "big nose" perspective distortion effect, something not generally desirable in portrait-type shots. On a 1.6x body you could get away with it for some full-length shots, and of course group photos, but not portrait-type work.
