So you want a single stroller?? Peg Perego P3 is your stroller. It doesn't fold like they typical stroller. Do you remember folding paper in hamburger an hotdog style? Most of the strollers are hamburger, a Peg is a hot dog!!!! It fits nearly everywhere. So far there hasn't been a spot it can't fit.
I love it because it will fit most infant seats, you just need the strap (which you buy seperatly) to hold down the seat. There is also a stand where a toddler can stand. So if your infant (seat has to be up in order for this to work) is sitting, your toddler hold on to the stroller and ride along.
It goes most anywhere. I haven't tried it in mud ( I wouldn't walk in mud anyway) but i have used it on gravel, grass, cement, the mall (it steers soo nicely). OH AND IT STANDS UP WHEN FOLDED!!! I always forget about that, but love it when I'm juggling everything, but I don't want the stroller to just be laying in the dirty parking lot.
http://us.pegperego.com/babyproducts-catalog/2011/Pliko+P...
It is pricey if you get it at a normal retail store. I got mine, brand new, on ebay for $170 which is about half off, and I got free shipping. Check them out! I love this stroller!
Oh I have had my 3 year old, very heavy nephew in the stroller and he loves it. He usually begs to be in it wherever we go anywhere.