If my math is right, a 6 amp toggle switch will handle a little less than 110 watts and should handle nearly all engines you would store on the track. An issue may be if you are storing a train with multiple passenger cars with older incandescent lighting and 2 or more powered engines with sound and smoke. That could draw more than 6 amps.
I use 10 amp SPST toggle switches for most of my engine storage tracks. I run the hot/red wire from the transformer to the SPST switch, and then to the track. I've never used a double pole isolation switch (no need for most household requirements). Since the common does not need to be turned off, can you just connect the hot wire to this switch and not the common? Better yet, return these switches and get a 10 amp SPST switch.