One of my all time tips for buying vintage and second hand is to not fixate on sizes.
Sometimes a dream piece is a few sizes too big or too long or maybe just slightly out of fashion (shoulder pads, looking at you). So the best solution is to take it to a alteration service, preferably one that can also do dry cleaning with eco friendly products. I recently discovered 1 Stop Wash in London that those all these things. Few months ago I found a vintage Christian Dior piece that was about 3 sizes too big and looked worse for wear. I took it to 1 Stop Wash and they had it altered and dry cleaned and voila! Perfect vintage blazer.
Highly recommend their service and you can find them at 100 Caledonian road London.