I have a sit-n-stand plus and I love it! There are several places that sell them but they are all about $160. This is not where I got mine, but it can get you the info.
http://www.onestepahead.com/catalog/product.jsp?productId...
We just took the back seat off for m y3 year old and my 1 yr old is still in the front. It was great with an infant because the kids faced each other and I sould see my baby.
My oldest took care of slipping blankets and falling pacifiers and toys and snacks.
Now we can even get 3 kids on it. 1 in the front seat, one on the jump seat sitting forward and another standing on the back! it is great for trips to the park with a friend or to hold a large diaperbag or backpack.
Good luck! and happy mothering.