Welcome to the forums @MC333.
You see what happens here. You ask a simple, specific question (how do I get to the post office?) and you get taken to far flung corners of Pentaxland that you didn't know existed! It's part of the charm.
Some great answers. @Na Horuk has summed up a wealth of learning and experience.
Let me just add my experience. I fiddled with a manual focus lens (Pentax-A 50mm f1.7, one of the ancestors of the DA 50) and extension tubes. For me, it was more trouble than it was worth - but then I'm not keen on stop-down (manual) exposure metering. I ended up with a dedicated macro lens (DFA 100 WR). It does double duty as an excellent fast medium telephoto prime. The only downside of them is cost (although I have seen some of the excellent Sigma 105mm macros sell secondhand for about $200 recently).
For low cost and uncomplicated dabbling, I think your original idea was right - a close focus filter on your DA 50. I would suggest getting a Raynox 150 (about $70) rather than the $20 set. Much better optically, and you can use it on a variety of lenses. People get some amazing results with it:
https://www.pentaxforums.com/forums/122-lens-clubs/74221-raynox-macro-club.html The Raynox pairs particularly well with the very popular DA 55-300 (lots of thread about this), which is about the best value telephoto zoom available.