I bought an Orvis silk top off ebay, which arrived today. It's for my holiday in June, so I thought I'd get away with an XL by then - it was worth a try for about £5, including postage.
So today it came, I tried it on - and it fits! It's roomy, it doesn't cling to the bumps. To be in anything that's only 1XL is just phenomenal! woohoo