The first mishna of Yoma1 explains that before Yom Kippur, a substitute wife is prepared for the kohein gadol lest his wife die -- because the torah says he makes atonement for himself and "his house", and "his house" means his wife. But he has to be married to exactly one woman on that day because it says "house", not "houses".
The g'mara on 13a-b describes a system of conditional gittim (bills of divorce), but I'm having trouble understanding how this actually works. Do I understand correctly that he takes an additional wife before Yom Kippur, with gittim written such that he will be married to exactly one woman when he performs the avodah? If so, does it have to be a different wife each year because of the laws of divorce and kohanim?
Since he could (in an unfortunate turn of events) end up married to the substitute, it seems like everyone involved would want to take as much care with this match as with any other. Yet, finding a good (and different) shidduch every year seems challenging, perhaps burdensome, especially as each must be a betulah. Is that just part of the cost of being kohein gadol, or am I misunderstanding this g'mara?
1 in the Bavli. The Yerushalmi understands this as a conditional marriage to the second woman rather than a conditional divorce (h/t Fred), which would reduce but not eliminate the problem.