I have decided to get my booster of the Pfizer vaccine and am scheduled to get it on Monday, November 29, the soonest day that was acceptably convenient with regard to my concerns about side effects the next day.
Reasons for the decision were as follows. I'm fairly confident that I'm making the correct decision to get a booster very soon. I'm less confident as to whether I'm choosing the best booster, but I don't think that's likely to make a big difference.
Decision to get a booster very soon
The new Omicron variant increases my risk from covid over the time frame of the next few months. I want my booster to have a substantial effect before Omicron becomes highly prevalent in the US. This was my main motivation to act very soon. I had been tentatively planning to get a booster within the next week, but may have put it off for longer before learning about Omicron.
I learned about original antigenic sin, which makes the concerns about waiting for a vaccine specific to new variants less relevant.
The CDC reported yesterday that covid boosters have less side effects than the second shot, which reduces the credence of the hypothesis of a lifetime limit on mRNA vaccines and also reduces my short-term concern about dealing with the side effects of the booster.
Decision as to which booster to get
Since I now want to get a booster very soon, the possibility of traveling to get a booster not available in the US is no longer appealing. And the risks of traveling are greater due to Omicron as well.
Convenience -- the first place where I went to book a booster (Walgreen's near my house) only allowed me to get a booster of Pfizer since my original vaccine was Pfizer. (In reality, this may have been the biggest reason.)
Getting a booster of the same vaccine as the original is the generally accepted establishment medical advice (based on Walgreen's requirement and also my doctor's advice).
The study referenced in this comment shows weak evidence that a Pfizer or Moderna booster after first two shots of Pfizer is more effective than a J&J booster. But Moderna might be the most effective of all.
Getting the same vaccine as I have already gotten in the past is dealing with something that's more of a known quantity to my body. It seems less likely that I would have unusual side effects with the same vaccine as compared with a new vaccine that I haven't tried yet.
Getting a booster of the same vaccine puts me in a more widely studied cohort, as noted here which might means I'll have more information relevant to my situation going forward than if I boosted with a different vaccine.
I have some thoughts that it might be better to get a J&J booster anyway since it is less likely to hit the lifetime maximum mRNA issue, or because it might do better in stimulating other areas of the immune system besides antibody production, but that is balanced out by the reasons above.
After a bit of research, I did not find any articles about a lifetime limit on mRNA vaccines. [Edit 1 -- found an article. See section 184.108.40.206. But it's an expert opinion submitted in connection with a lawsuit] [Edit 2 and the authors are affiliated with an anti-covid-vaccination group so
has a stronger likelihood of bias as compared with a journal article. So it is likely quite biased.]