Betaine HCL is good but pricey.
If you want fast results I would definitely go with Jarrow B-Right and omega 3.
Brewer's yeast or whey is also good because low stomach acid cause subclinical protein deficiency. Free amino acids are superior to other forms of protein.
Low stomach acid is often caused by adrenal dysregulation - HPA axis dysregulation as part of the Autonomic Nervous System dysregulation. I also wrote some blog posts about digestion, ANS dysfunction,etc...
Forskolin is one of the best herbs one can take to raise stomach acid.