My suggestion would be to get a Brooks B66 or B72. The vinyl mattress saddles I've used lead to OMAA syndrome. I tried to ride my Triumph with its old mattress saddle, but quickly gave up and replaced it with an old B66 I bought on eBay. Much better.

Chain Reaction has sales on saddles on occasion, and the price is quite good, even with shipping, if you want to buy a new one. Right now the B67 in Dark Green is on sale. You can use this saddle with a mounting clamp on your old sports.