1. Bite the bullet: we are most likely not even a computer simulation, just a mathematical construct[3]

Biting the bullet here is roughly equivalent to accepting Tegmark's Ultimate Ensemble. This was discussed on LW in ata's post from 2010, The mathematical universe: the map that is the territory.

See Tegmark (2008). In particular, Section 6, "Implications for the simulation argument". A relevant extract:

For example, since every universe simulation corresponds to a mathematical structure, and therefore already exists in the Level IV multiverse [the multiverse of all mathematical structures], does it in some meaningful sense exist “more” if it is in addition run on a computer? This question is further complicated by the fact that eternal inflation predicts an infinite space with infinitely many planets, civilizations, and computers, and that the Level IV multiverse includes an infinite number of possible simulations. The above-mentioned fact that our universe (together with the entire Level III multiverse) may be simulatable by quite a short computer program (Sect. 6.2) calls into question whether it makes any ontological difference whether simulations are “run” or not. If, as argued above, the computer need only describe and not compute the history, then the complete description would probably fit on a single memory stick, and no CPU power would be required. It would appear absurd that the existence of this memory stick would have any impact whatsoever on whether the multiverse it describes exists “for real”. Even if the existence of the memory stick mattered, some elements of this multiverse will contain an identical memory stick that would “recursively” support its own physical existence. This would not involve any Catch-22 “chicken-and-egg” problem regarding whether the stick or the multiverse existed first, since the multiverse elements are 4-dimensional spacetimes, whereas “creation” is of course only a meaningful notion within a spacetime.

A while ago, I posted a LW discussion link to John Regehr's blog post about similar ideas: Does a simulation really need to be run?.