Dan --
When it comes to lather bowls, K-Mart, Target, Wal-Mart, (similar discount chain stores in the UK) and the like are your friend. As a general rule, lather bowls are best when 4.5~5.5 Inch (114~140mm) in diameter, 1.75~2.75 Inch (45~70mm) tall, stoneware (to retain heat/warmth), non-white interior color (so you can see lather develop), glazed but with a roughened surface (to aid in lather building), and CHEAP ($2~$5 (£1~£3) so you have more money for other shaving goods). Color and decoration to suit, with or without handle to suit.
I think that about sums it up.
Most 'purpose' made soap or lather bowls from shaving suppliers are overpriced, fail on most counts above, and are simply inadequate.
Good Luck.
-- John Gehman