mulm, sounds better than poop & debris
using an airhose tubing as a siphon is a fast way to suck it out immediately, then try not to disturb the substrate anymore. Which is impossible to do when you move things around and that can be unavoidable. In which case, you'll usually want to do the airling tubing trick again and do a larger water change to deal with the ammonia spike.
When using the regular siphon, you can avoid stirring up the mulm by using a differently technique, that doesn't send the debris up anywhere but into the siphon itself. And be sure to add water back into the tank slowly, onto a rock, your hand a plate, etc. so as to not stir up the substrate more.
Bottom feeders are also a good idea to clean up any uneaten food that's fallen. Pygmy cories are adorable... they tend to school and have great personalities. Then are constantly cleaning/moving, and playing.
Last, increasing your water flow is another option to increase filtration. It's important to consider the amount of flow with what types of fish you have. eg. bettas usually don't like strong flows.
I'd try the airline trick, then siphoning/water change methods that don't stir up the gunk to see if that does the trick for you first. Then after water conditions are better (ammonia is back to zero) than you can consider adding some cories if you'd like. I'd wait on a new filter at this time... if you want to spend money on something, maybe consider investing in a second bulb for your light if possible to bring you up to 2w per gallon and let healthy plants help with your filtration.