Arrgghhhh so many choices. My toddler is on the very edge of outgrowing the travel system, Ive been looking at either and Out n about nipper or a mountain buggy. However we are TTC and I think we'll need a double at that point, do I buy a single or jump straight to a double? I was hoping to eek it out a bit longer but they have different ideas. I think the mountain buggy duet can be used as a single?