This sounds so exhausting for you, I have to say that my case was not as bad as your by the sound of it. It cleared up on 10 days of Flagyl and then when it reoccurred it cleared but then I went into a bad flare. My UC has been less controllable since though :-(
In answer to your questions:-
VSL I did get just for one month from my doctor, normally they are not allowed to prescribe it here for anything but pouchitis. It did really help me after the antibiotics but after that I think it stopped doing much.
Florastor - I think that is s. boulardii? I did take that and I once made myself an enema of it. I think it helped but I kept to very small doses because I have read it can get out of control and cause fungiciema if you have too much on a compromised immune system. I also kept up my mesalazine as Borody as said he thinks it has some action against C diff.
My stool tests were negative too. The first time they indentified it through a scope (yellow, ***** ulcers) and the smell was terrible. The second time I had the same smell.
I virtually never take pain pills so don't know about
that although if they have any form of opiate in them they will of course slow the bowel. I was brought up in a family that were anti-pain meds and a culture of, if there is pain, listen to it, it is telling you something. I try to use mindfulness to manage pain. I don't think I've suffered as much pain as you though by the sounds of it.
I would not touch salad personally while ill and even not when well unless I know its source, not only because I cannot digest it (too much water for the bowel to deal with) but because salad is one of the most dangerous foods in terms of food poisoning risk. www.nhs.uk/news/2016/11November/Pages/Bagged-salads-pose-salmonella-risk-says-researchers.aspx
If you do eat salad be sure to wash it well in a vinegar solution. I lightly cook my veg. Broths are excellent because you catch all of the nutrients in the broth. There's some silly propaganda that goes around about
raw food always being healthier. I've read a lot of studies and it is not the cause. Minerals are not destroyed by heating and some nutrients actually become more bioavailable in cooked food. Some vits are destroyed by heating it's true. Interestingly, frozen veg lightly cooked immediately from the freezer retain more vitamins than some salads that have been stored for a while since harvest.
I understand that is scary being so ill. I would push for FMT, it has a massively higher success rate for C Diff than any antibiotic.