English brands that are good for wide horses include Duett, Thorowgood Broadback or Cob saddles, Wintec Wide saddles, Black Country, Lovatt & Ricketts, some Albion, some County, and some of the Thornhill saddles. You want one with a "hoop tree". They do better on wide horses.
Those "draft tree" Aussies and English saddles on eBay should be avoided. Almost all of them are Asian made junk. The only mid-priced Aussie saddles I would trust are Wintec's synthetics and those form downunderweb.com, and I don't know if either would work for a draft horse.
For western saddles, both Abetta and Big Horn made draft saddles. I believe Big Horn's is labeled as a "Haflinger" saddle, but it will fit drafts well too.