Tailoring shirts is certainly not an easy craft, but if your shirt fits you well around the shoulders, it's very easy to adapt the waist hem to your body.
First, practice with an old shirt. If you get a good fit once, you can repeat the same process with any new shirt.
The easiest is the pinch method (see it in action here):
Put your shirt on, but inside ...
If you're going to get some new shirts, buying the shirt material and getting stitched from a tailor according to your size would be the best way.
You could also get your old shirts altered from a tailor.
There are also some hacks like
Doing a military tuck
Using shirt garters. These help in keeping your shirt tucked in. If you again find excess material, ...