Ordinary multi purpose, with or without peat, with or without a percentage of John Innes mixed in - any of these will do the job.

Thanks Bamboo. Would it be worth mixing in some water retaining granules as well?

I just realised I should have said 'ordinary multi purpose .... POTTING compost' - there are other composts not intended for use in pots, of course.

Yes, you can if you want to. I never bother personally, but it depends how attentive you can be to watering later on as to whether its a useful addition or not.

Thank you Bamboo. That's a great help-at least I know what to get and will have minimised the confusion that always ensues! What do you prefer -terracotta or composite (plastic) plant pots? I prefer clay or terracotta but always worry they might crack in winter or get very hot and dry out the soil.

I like terracotta - but I'm sick to death of years of broken terracotta pots, so now mine are mostly plastic, some metal. You've always got to check whether terracotta is frost proof or not before buying - and they will probably need more watering because they dry out quicker, being porous.