The saddle pad has button holes and the MER can be purchased as a breast rug or quarter rug...or complete set. The rugs attach via toggles onto the saddle pads, then you can happily ride & the rug sits securely.
Please note as the sizing is European measurements need to be taken from the wither to the top of the tail. A 5'6 horse usually wears a 125cm, a 5'9 in a 130cm, a 6'0 in a 135cm and so on. It's best to measure your horse especially if longer or shorter bodied. :)