A word of caution for the Buggy Board attachment. All strollers have weight limits - Maclaren strollers are the only ones rated for 55 lbs., almost all other ones are 40-45lbs; therefore, you put a baby in the seat and a 5 year old child on the Buggy Board and you are most assuredly over the weight restrictions for that stroller. Your kids weight 70lbs, combined, which is too heavy for one stroller. I'm sure the fact that the Buggy Board says it holds up to 65lbs will confuse people, but this is only talking about how much weight the Buggy Board can hold, and NOT the actual stroller.
I'm not sure how Health Canada would allow this type of attachment to be used when it doesn't seem to be very safe at all. Its sole purpose is to have toddlers or children stand on it while another baby is in the stroller, but this means that parents better know the weight restrictions for their strollers or there are going to be serious safety issues with the stroller.
Good luck in your stroller search - as someone mentioned, a double stroller, or the Sit and Stand or Peg strollers that are specifically made for this purpose (they can carry the extra weight in the back as they are made for this purpose, but they too have weight restrictions) are your best bet as add-on attachments made by other companies are usually never a good idea. The price of this attachment alone is outrageous as you can get a new Maclaren stroller for that price that will hold a single child of up to 55lbs!
Tiger