Am reporting back here on plan A, which was to buy a replacement strap for my chest-based HRMs.
Bought a “PowerLabs” strap from Amazon. It specifically says it is not compatible with 2020 Wahoo Tickr, and it does not mention Bkool. It states that it’s snaps are spaced at 1.75" – which would be 44.45mm – and it has almost zero flexibility between the snaps.
The Wahoo Tickr (5 years old) seems to be spaced at 45.24 mm.
The Bkool (4 years old) seems to be 46.04 mm.
The strap fits the Wahoo Tickr fine. In fact, one nice thing about it was how the snaps on the strap protrude a little. That helped when going onto the Wahoo snaps, since the Wahoo snaps are sort of recessed.
The strap does not fit the Bkool. It can be snapped onto the Bkool, but due to the larger spacing between the Bkool snaps, there is so much tension created in the strap by the extra 1.5mm that it immediately unsnaps itself.
By the way, regarding plan B, which was to buy a new HRM altogether, I’ve decided to try out a CooSpo armband. Yes, most people responding to this post really seem to consider Polar to be the best brand, but those are twice as expensive, and it’s hard to say whether a Polar would be twice as good as a CooSpo. (To assess what “twice as good” means, I’m considering three metrics: longevity, connection reliability, and battery life.)