A swallow is one of the narrower Brooks saddles. We don't know what kind of width your sit bones are.
Every one is different, so no one would be able to 'confirm' whether a Brooks Swallow would be comfortable for you or not.
SA's do sometimes seems to have that stretching problem. Brooks don't have that as far as I know...the leather is much thicker for one thing.

If you buy from Wallingford, you can return the Brooks after a couple months test, -as long as you don't apply anything to it but Brooks' HydePruf.
If your average ride is over 50 miles (!) then it sholdn't take you long to figure out if the Brooks will work for you.
Because the Brooks is thicker and stiffer than SA, expect a longer break-in period though, and you might feel sore sit bones for the first few rides.

If your sitbones are not all that narrow, then you might want to consider a Brooks B17 instead of the Swallow. I usually see thin guys with skinny-teeny butts on Swallows.