I sold a ton of belts for mowers when I worked at our company's front counter. Aramid/Kevlar wrap is critical on a mower deck for longevity. Also help keep stretch down. We stock Continental (Goodyear) #84620/#20034404 Kevlar in a 62" for $18.00.
Does the deck have a tension pulley? Did you check the spindles for free movement when you had the belt off? Honestly, the .375 in the OEM length should be irrelevant.
The simple way to measure a belt is to mark it with chalk or something...straight line across back of belt. Then, just use a standard tape measure and walk it around the belt. It's not ultra precise, but I didn't have many comebacks on the couple thousand that I sold.
As far as the "best" belt out there...unsure....the one that fits is a good start though.