I don't think a break beam is even necessary. Put both components on the same side and let the hand reflect. Same as on all those LED coffee tables. The simple modules I've built that were purely analog in design, only required a handful of components. With an MCU, an IR LED and an IR photodiode with a few resistors and you'll have a very rudimentary proximity sensor perfectly suitable for your project that will be easier to hide if you put them next to each other and use reflection instead of break-beam config.