The biggest brush I have is a 26mm Rooney #1 large in silvertip ($150 at classicshaving). It is not floppy, but isn't dense like a Simpson either.

I can't see myself going to a bigger brush - as I use soaps a fair bit and find a 26mm brush a bit big.

If you want a big brush, you might want to consider some of the Saville Row brushes - there's a 30mm best/super badger for about $85 (supposedly a rebadged Kent) and there's a lightbulb-shaped series of silvertips - I think the 28mm goes for about $150 and there might be bigger knots available on a variety of handles.

The SR brushes are great value and, IMHO, are a good combination of soft and dense - they work great with both soaps and creams. I like the lightbulb-shaped knots as they have a denser feel than the traditional fan-shaped knots of the same width.

Shavemac can also do a custom brush in just about any size you want (but it won't be floppy) for less than the BK12.

If you want a floppy brush in a 30mm or bigger knot, than I think Vulfix or Kent are your best bets.

This e-bay vendor has a brand new BK12 on for 95 pounds (vs 108 on the Kent website - although if you troll around B&B, you can find a discount code worth 10 or 20%) and very reasonable shipping:

http://cgi.ebay.ca/Kent-BK12-Shaving...QQcmdZViewItem

If you're looking for mopish/floppy, than you likely want a brush with a higher loft - for example the Rooney style #3 in large will feel floppier than the style #1 in large as it has a 10mm higher loft - notwithstanding that they are both 26mm brushes.

Hope this helps.