Thought I'd reply I know your post has been on a while and you have got no replies. I can only tell you what we have done. There are almost three years between my girls, but I like to walk a lot so had to have a pram to put them both in. I've got a Valco runabout and the todder seat takes up to 20 kilos so my 4 yo still goes in it. I am generally pretty happy with it as it is versatile, can be used as single or double,folds up easily and reasonable small. However, if possible I now put the baby in the front and toddler in the back as it is much easier to push with the weight in the back not the front.
We also have a Valco side by side umbrella stroller which we bought to take on holidays and use a lot, especially for the shops. It is wide, but still fits through a standard doorway so ok for the shops. I bought it for $100 off ebay - they retail for $250 new. Folds up almost as small as any medium sized umbrella stroller.
A friend bought a Baby love double from Babyco for around $300 and that works well for her. It is a three wheeler. Perhaps you could look on ebay for a secondhand double.
Sorry, but my advice is you might need to look for a new pram!
Michelle,SA,DD1 4 yo, DD2 9/8/05