My early quick post was just so I could mark the thread.
Tim Spector runs a Gut Project to analyse samples – not sure of the cost but could help you.
britishgut.org
OH's been advised to go on a low residue diet – no fibre – which is against normal advice, becasue we're all different, for example, both of us have extensive diverticulitis which gives OH great problems, but not me.
However, we are fortunate, as not only are we retired, but both can cook. We avoid processed food as much as possible, make our own hummus but leave out tahini, tabasco, neither good for OH, make our own bread as modern bread appears to have increased the incidence of coeliac dramatically.
We feel for you Limb, and think you're being so sensible in trying things out to see what makes a difference. We've taken note of some of the suggestions here for ourselves.
In the AMA section is a dietician who is willing to answer anyone's questions.
A vegan friend of mine assures me his diet provides plenty of protein and other nutrients, so vegetarian diets should do as well. He doesn't search for meat substitutes either.
We wish you all the best in your search.