Since you have a crop sensor, and weight is a huge concern, I'd highly recommend you consider an EF-S mount lens. There are some extremely high quality ones that most people overlook since they don't work with full frame sensor cameras. Since they are designed to work with a smaller imaging sensor, they are able to be smaller and lighter than their EF equivalents. Here is a general purpose ones that might suit your needs.

The main downside is you'll be losing some of the focal range you're used to with your current lens, but you should see a drastic improvement in photo quality! With the high resolution of the T6i, you can crop somewhat heavily to add more zoom if you need it ;). They don't have too many EF-S lenses, but they have a macro one, a wide angle one, a telephoto one, and the one I linked to. If you're fully committed to sticking with a crop sensor for the foreseeable future, they're a great bet!