I have not read the entire thread but you want to prevent your exposure and you want to take the best treatments you can.
Hydroxy was hyped as an easy answer, it failed in legitimate testing. Actual treatments such as steroids and a few others have passed scientific testing.
The vaccine works well for the original strain and worked quite well against Delta. It works reasonably well against Omicron. The issue is that the vaccines target the spike protein, if here are too many changes to that protein in a new strain then the vaccine loses effectiveness and enough change makes the vaccine unable to confer protection. Omicron is a quite changed spike protein but not changed enough to evade vaccine based immunity but enough to reduce it. Pfizer said they can have an Omicron vaccine ready by March.
That said if you are immune suppressed and your body can't crate antibodies then the vaccine will be useless as the point of it is a non toxic exposure to one piece of covid to build immunity for so that future exposure results in immediate immune attack instead of taking two weeks to create the correct antibody.
This also means your body probably can't create antibodies against covid meaning you are far less likely than the non immunosupressed to survive
I would suggest KN95 or N95 masks. Even tight fitting eye goggles (eyes can allow the virus into the body but is unappreciated compared to nose and mouth). Cloth masks in theory filter out some covid, but are not great. Ideally we would all wear N95 masks properly fitted. That would kill covid quickly if we all stayed masked around others.
Covid is an aerosol and floats around, Omicron even more than previous strains. The masks are a filter. If someone breathed unmasked and has covid then its in the air nearby and its on items in front of them and they touched. When you buy products put them in covid quarantine for a few days.
So the restaurant where you are 6 feet apart but eat unmasked is not good enough for Omicron, Frankly its often not good enough for the older variants.
Outdoors helps because aerosols disperse faster in larger volumes of air but if getting infected means you may not live then its not good enough either.
So when you touch something outside your house or items not out of covid quarantine (give it 3-4 days) consider your hands contaminated and whatever you touch will become contaminated unless you used hand sanitizer or washed your hands with soap. Also when you remove mask/goggles consider them contaminated by others and keep them away from other items and wash your hands immediately (or hand sanitizer when away from home).
So hopefully some of this helps.