IMHO I would definitely get some of the weight off. Then Look for a new saddle.
Also when looking for a new saddle I might consider a McClellan Cavalry Saddle. I know they look like a death trap for the ol' butt but a seat saver can do wonders. You can get them pretty cheap of of ebay
right now. Last I checked good quality ride-able M1904 Mac's where selling for around $200-$150-even $100. At that price if it doesn't fit you can always re-sell it for at least the price you paid for it or just keep it to admire as a piece of history. But I must warn you to stay away from the Royal King civilian style mcclellans. THEY ARE BAD. Some may say that a original mcclellan wouldn't fit him which may be true if he's really fat but I have been surprised when a original mcclellan fit my fat wide backed arabian. NO joke. Just my 2 cents though, hope this helps!
PS. I've seen alot of gaited people ride in McClellans too.