If you are looking for fashion, try Limbo in Annankatu or Rosebody in Yrj nkatu. Union Five in Erottaja is a mecca for the youthful and fashion conscious. Finns have an international reputation as designers of outdoor wear that is both warm and light and looks good. You will find excellent selections in the big city-centre department stores Stockmann, Sokos and Aleksi 13. Design Forum Finland's exhibitions in Fabianinkatu give a good idea of what is happening in the world of design.
Articles are also on sale there.
The Museum of Art and Design and the Museum of Contemporary Art Kiasma are absolutely worth having a look at, and they have fine shops. The staff at these museums are good people to ask about other places to find good design in the city. They know what is around and will be happy to point you in the right direction. Ask the Tourist Information for more tips, and don't be shy about dropping into the shops to see what they have. There is neither an obligation nor any pressure to buy.