Have you tried Macbaby which is very clsoe to your location, otherwise Manor in Letzipark. If you have a car, in Spretienbach there is a good baby place, turn left to goto Coop, Media Markt etc... then it's on the left after the 'new junction' (can't remember the name).
Try the second hand clothes shops near you(should have baby section) and also try www.ricardo.ch, you should find a cheap winter body warmer for your baby or winter sack for your stroller. Good luck!