Sherr have a look this RSPB link, all sorts of feeders to choose from. Just don't put them where cats can hide nearby such as under bushes etc. High up is best, near a tree, so that the birds have a somewhere to hide quickly if they see danger.
Robins will come to window feeders but wrens won't as they usually peck around under hedges etc. Sunflower hearts will attract all sorts to your feeders as many different birds love them.
https://shopping.rspb.org.uk/bird-feeders/