Welcome!
As stated by others, most new European pipes take 9mm filters. Adapters are very cheap and bring the draw down to 3mm if you would rather not use a filter. As far as filters go there are a lot of options but I prefer the Stanwell charcoal ones (when I use one).
Many Savinelli pipes are made for 6mm rather than 9mm filters. The Savinelli filters are balsa wood inserts. As with 9mm pipes, cheap adapters are available to bring them down to 3mm if you don't want to use the balsa inserts.