I ride in a poley saddle (that's what they're called...the name comes from the panels that stick up in the front that hold you in = poleys). What's nice about a poley saddle is that the Australians actually designed the entire saddle with a purpose, taking the best of English and the best of Western and a little of their own. I did a lot of research on these when I got mine. I figured that, just like an english saddle, there must be a proper way to ride this thing. So, I didn't want to just plop it on my horse and ride western...I decided to learn to ride "Australian"...not surprisingly, there is actually an Australian method of equitation that goes with this saddle!! It takes a little getting used to, and sometimes you can hear/see the snobs "criticize" your equitation...but what do they know about riding Australian? lol
The underpad should be really thick and in a better made saddle it's flocked with a material that actually gets heated up by your horse's body heat and then it molds itself to the horse's back for a great fit. The only thing is that you do still have to make sure the tree is appropriate for your horse. The tree is about how and where the weight is distributed, so it's important that it not be too narrow or too wide, just like any other saddle.
English riders usually have no problem adjusting to the seat because a poley saddle is a forward-seat saddle, just like English. Western riders try to sit like they do in a western saddle and often find the saddle to be uncomfortable...because they're sitting in it wrong. If you don't sit like you sit in an english saddle, it'll actually get more difficult to ride as the horse goes faster. The faster the horse goes, the more the saddle is designed to pitch your forward. At a full gallop, you should almost be half standing and leaning forward. In Australia, they still use horses to wrangle, but the terrain isn't quite the same as the open flats of the American cattle west. So, riding involves tops speeds in an unforgiving environment and terrain. Getting up off the horse's "drive axle" (his rear end) and up over his shoulders (as opposed to sitting erect in a backward seat) makes much more sense and is a lot safer when you have to go up and down hills at those speeds. Think about the jockeys...how they ride to get their horse to go as fast as possible. The poley saddle is actually designed to "help" you get into your sort-of two-point position. If you try to sit back in it, it won't be very comfortable.
Another thing that Americans don't realize (and have trouble with) is what to do with their feet. Yes, it's a forward-seat saddle, but your feet don't go underneath you. They actually go slightly in front of you. So, your body is set more forward, AND your feet are in front of you at the same time. You're also supposed to put 25% of your weight in your stirrups as you ride. If you try not to do this (and completely sit as you would a conventional saddle), the saddle will kind of push you forward at the trot, which you're supposed to post. The reason you stand in the stirrups a little and have your feet out in front of you has a purpose, too. Again, it's because of the terrain. If the horse stumbles or goes down, your feet in front of you are in a perfect position to catch you so you don't get hurt. You're already poised to basically "step" out of the saddle if that happens.
The reason that poley saddles are the way that they are is because being a cowboy in Australia is actually one of THE most dangerous occupations in the country (if not THE most dangerous). The reason is because farms are massive...hundreds of acres a piece. There's not much grazing land for the cattle, so the cattle are allowed to wander. Where the grass is, there are no people. If your farm is fortunate to have an airstrip, if you get hurt, there might be hope for you. But you still have a long flight to a hospital. If there's no airstrip nearby, it'll be days before a doctor can get to you and you'll be dead in the mean time. It's not the snakes or the crocodiles or the dingo or whatever...it's the same risks that we have here - riding is inherently dangerous, and accidents happen there just like here...except there's no help when they happen.
Anyways, didn't mean to write you a book. Have fun in your saddle! =D