Dr No[Moderator Omega - Wristscan]
37541
Another appealing option . . .
. . . would be Omega's double-ridged sharkskin strap . . .

. . . seen here adorning a Speedmaster. Omega offered these straps when your SM 300 was in production, but they've been out of stock for years.
If you can find one, get it!
Best,
Art