So, thanks for all the answers, I did use the seed generator all afternoon but alas, nothing realy buys it for me.
By large island, I don't mean the longest but rather the most round. My standard would be at least as large as the star-shaped meadows that appears around the spawn, wich you can see when you choose to show only the biomes layer.
So far the best seed I found was XvPf2Zdmzs, so still not quite enough for my taste.
I checked "a" "OOOOOO" and ''OOOOOOOOOO" and I quite like the second one, I'll check it out.