Ugh I absolutely FEEL you! I had chronic heartburn before I got pregnant and then it got just out of control. A few recommendations....
Most Providers will tell you to steer clear of baking soda as it can actually cause systemic alkalosis. Not good.
Though ACD may help some people, the reason heartburn increases during pregnancy is that the increase in estrogen causes the sphincter above your stomach to relax and thus stomach contents can more easily splash out causing the sensation of heartburn. In this case, there is no underlying issue with overproduction of acid so ACD may simply make things worse, but everyone is different.
Papaya enzyme is very popular with the pregnant peeps, Give it a try! However, with my underlying GERD, it really didn't help.
If you are waking up in the middle of the night choking on acid, please speak with your provider! I understand the desire to avoid meds, but this is a serious risk of aspiration and could easily send you into the hospital for aspiration pneumonia. they may simply recommend raising the head of your bed :) seriously.
Tums may seem like a holistic option, but taking them too often basically keeps you from digesting your food because it lowers the pH of your stomach so much.
The only thing that really helps me is zantac (ranitidine), and I have tried it all. It is safe to take during all stages of pregnancy (and yes there is human research to back this up) but of course you should check with your provider first. Also dietary restrictions, tomatoes, chocolate and caffeine of any kind gets me every time.
Good luck with it ladies!