I don't have a working 1B anymore, and I've always used Pis mostly headless, but when I did use a GUI on the original Pi I would use FVWM with no DM. I'd boot to "multi-user" (ie., a text console), then login and
The full GUI stack (really, just X + FVWM) took about 150 MB of RAM, leaving enough room for apps. Mind you, I did not use it for serious programming or web browsing, and TBH I think the default LXDE was not much heavier.1 I do not think the 512 MB versions have enough memory to do the latter comfortably, especially if you are running some kind of IDE as well.
I don't recommend FVWM specifically as making it really useable requires a lot of familiarity, but the general point is you can use Raspbian, either starting with the light version and installing the GUI stuff, or the full version, install an alternate window manager and just change the configuration. More about that approach, with some details of how the linux desktop stack is structured, here:
I don't know what the current state of lightweight, potentially stand-alone window managers is today, but if you research this in relation to "linux" and not "raspberry pi" you will find more and better information. Anything along these lines that can run on a normal linux box can be installed in Raspbian (or any other distro), memory and performance permitting of course.
- I also tried XFCE a bit, which was okay; I preferred my customized FVWM better anyway. Note that the current default Raspbian desktop is a spin off of LXDE.