It was posted elsewhere on here that it's not a great idea to pair aluminium bodied TPMS sensors with steel wheels, because of the risk of differential corrosion. Personally I'd go with 16" alloys. In the UK I'd look at https://www.oponeo.co.uk, who, I'm sure, operate in Europe too. As to tyres, Nokian are a reasonable and not too expensive brand, but http://www.tyrereviews.co.uk has lots of tests and info.
ETA: Re TPMS, if you don't want to swap the TPMS valves over, or get your dealer to code the winter wheel ones to the car, and back again in summer, then it would be worth investing in one of the devices available to clone TPMS sensors, so both sets of wheels have the same codes. Autel do a TS401 that will do the job (no need to reprogramme the ECU) plus their own sensors at around β¬25 each.