I want to be able to press a button to increase a signal's strength by 1 and press another button to decrease it by 1. I have thought about making 15 t flip-flops, but that sounds like a difficult way of doing it. What is a better way to do this?
This is probably the most compact circuit of this type; it additionally can accept pulses on any length on both inputs and provides symmetrical signals, x and 15-x on the two sides. The only downside is that you need 18 stacks of any 64-stackable item, to completely fill the droppers under the repeaters - the other droppers are to be left empty. Both repeaters should be set to 2 ticks.
This circuit should also work on Bedrock Edition, with the small modification - add solid blocks on top of the empty droppers to power them through these blocks - on JE they can be powered through quasi-connectivity.
I have found a viable solution: Signal strength memory
It does exactly what the description says, except the "button" has to be exactly 2 ticks or it will increase/decrease too much. A simple pulse shortener should sort that out.
Here is what it looks like as well as a layer breakdown: