The amount of memory does not mean lightweight, in reality lightweight is addons that use low CPU cycles, in combat this is most noticeably if you run a lot of addons that eat CPU cycles, you get lower fps. Just having an addon use 5MB memory all the time doesn't mean it's not lightweight. :P
Point is, all the addons you mentioned, even Bagnon (I use) are not so "high tech" that you need a more, function wise, limited addon. You can disable the bank modules and just use "Bagnon" (the main addon) to only handle bags and character bank frames.
I can't speak for all addons, but for Bagnon I know you can configure to appear very simple and feature-less, i.e. give you the feel that it's simple. :P
I just don't want you to think lightweight is directly correlated to the memory an addon uses!
