Aussie saddles are incredibly secure, and I agree about the barrel saddle-- my everyday Western saddle is a barrel saddle with a suede seat & fenders, and although it gets dirty easily (frequently blue from my jeans...) that saddle may as well be crazy glue!
Another option is to pick up a grab strap for your english saddle... they look like this... http://www.arcaros.com/images/products/detail/6607.JPG
...and are a cheap solution in the "having something to hold onto" deparment. Also-- wear full-seat breeches! Those will help you stay stuck.