The advice you have been given is correct, namely, that the lights are not switched on permanently and they appear only at times of their own choice. They are more frequently visible the further north you go and there they are also more intense. They are visible in all countries far enough north and in each of these countries they are more or less equally frequent at any given time. When visible in the UK and similar latitudes they are rather feeble by comparison. To see them you are best to be away from built-up areas, the sky must obviously be clear and it must be dark: You only see them in winter although what gives rise to them is still going on all year around. The very same phenomenon (aurora) is visible in the southern hemisphere during their winter. None of this is, nor has it been, in any way a secret although not everyone takes notice.
Your choice of place to try for a sighting (I assume you have in mind a short visit - a longer stay comes closer to guaranteeing a sighting) will depend on your preference on other things such as distance, cost, other things to do and see, etc. It so happens that the cheapest place to travel further north to from the UK is Iceland - Norway is more expensive to visit, Canada much further away, etc. I have visited both Iceland and England and the weather in both places is variable - in winter you need winter clothing in both places. Of all the places I have been to, I have never felt so cold as in England, and that was indoors. Everywhere you go in Iceland, be it airports, buses, bus stations, shops, offices, houses, etc. are warm at all times/seasons - that is nowhere near to being the case in any part of Britain. In Iceland, a jumper is classed as outdoor clothing.
I genuinely hope that you go and are successful in seeing the lights somewhere because a good display is something truly special - with most people the experience stays with them for the rest of their lives. I have been so lucky as to see some brilliant ones on more than one occasion. My wife has not been so lucky in spite of several winter visits to those latitudes. That's the luck of the draw.