I have had Gerd for 2 years now. My Integrative GI doctor initially wanted me on PPI's but I refused, so we started off with Zantac which proved only moderately effective at 150mg X 3 per day. It wasn't until he included the Baclofen that I noticed better control of my severe GERD, which included at the time esophagitis, LPR, and aspiration of acid in the lungs, particularly at night. My GERD was constant, and could not be appeased with dietary modifications. I also have UC, so like you, I have to be VERY conscious that my foods do not cause or exacerbate a flare.
I have not had any testing done to show a poor functioning LES, but my chiropractor believes that I do have a sliding hernia. I delayed testing after being diagnosed last year with severe Hashimoto's. My GP thought that the LES may be weak due to years of extremely low T3 and T4. But, unfortunately, after taking Levothyroxine for 8 months, instead of improving the reflux, my symptoms worsened, and I had to put myself on OTC Prilosec. I still take Baclofen 10mg X 2 per day; I take it in the morning with 20mg Prilosec and in the evening with 150mg Zantac. I am fairly stable, although I can not tolerate vegetables :(
I do not feel any muscle weakness from the Baclofen, nor any other side effects such as drowsiness. I do believe that if I were to remove this from my regimen I would not be able maintain my current stability. I think it is the Baclofen that allows me to sleep through the night without reflux.
I just thought that I would mention the benefit of Baclofen for my personal GERD symptoms. You said you didn't find it effective for you over the years, but I wanted to share that Baclofen has been very beneficial to me.
I'm sorry to see that your GERD is getting worse. That is indeed a most scary place to be, and I know that you want some relief. Maybe you could give the Baclofen a go again, at least until you can figure out your next move? I do hope that your issues resolve soon.