https://github.com/SukkoPera/OpenC64Cart

Such chips can hold up to 8 cartridge images, which can then be selected by jumpers. Other jumpers allow the selection ROM type and of EXROM or GAME mode, achieving compatibility with many different types of ROM, from "simple" games to Ultimax cartridges.

The recommended part is Winbond W27C512 (or W27E512, I don't understand what differences they have), which is widely available, cheap and electrically erasable, which avoids the need for a clunky UV-eraser. This is the only part that was thoroughly tested. Other parts, even smaller in size, will probably work, but will require an ad-hoc configuration.

Usage is straightforward: just insert the EEPROM in the socket making sure that the notch and all pins are aligned, set the jumpers as desired and plug the cartridge in your C64.