The snapback problem seems to be quite common among new controllers. There are a bunch of things you can do.
You could
1. tilt the stick instead of pushing it all the way.
This way, the stick won't have as much speed when you let go and doesn't snap backwards. This option has the added benefit of being able to push the direction and b at the same time without side-b-ing.
2. Keeping your thumb on the control stick when letting go.
You mentioned "returning the stick manually" - I don't really like the term since (to me at least) it implicates actively returning the stick to neutral whereas you can simply rest your thumb on the stick while letting go of it. The weight of your thumb is enough to stop it from snapping back.
If you feel like it's too slow, don't forget that the turnaround is buffered for a while after the input. So if you need to turn around quickly, you can do the input during the jumpsquat frames or at the beginning of your jump already.
3. Buy an older used controller.
Expensive and you're not guaranteed a good controller, wouldn't recommend.
4.
Apply silicon grease to the stick box.
So Kadano found out that applying a thin layer of silicon grease to the stick box adds a slight amount of friction that is enough to stop the snapback but is not noticeable during normal use. This is probably the best option since you don't need to change the way you do things and it's pretty cheap (<10$ for a triwing + silicon grease).
However, there currently isn't a dedicated tutorial on how to do it but Kadano mentioned he would soon do a full write-up on the procedure. If you don't want to wait for that, you can go to
his hardware thread, read points 2.0 until 2.7 and figure the specifics out yourself.