Lucky enough to have been on a couple of Norway cruises from Southampton plus a Hurtigruten Coastal Express cruise.
If you are looking for a departure port up North, may be book via a TA as they will know all the options. Have seen Fred Olsen sail from Newcastle and there's possibly a couple of others from time to time.
We've done 5 cruises crossing the North Sea for Norway/Baltics and it's been as flat as a pancake every time (hubby not happy!).
If you think you may suffer from seasickness, would suggest take a tablet on the day of boarding and listen to the updates from the bridge. They will give you advance warning of when they are expecting rough seas and this is when to take the tablets. If you leave it until you are starting to feel unwell, it's too late. Absolutely worst case, if you are suffering, you can head down to the medical centre for an injection. It will cost but have heard it works according to parents friend! Whilst mum/dad are good travellers, their cruising buddies aren't and they've done the above for the last 35 years and as long as they've taken their tablets, they haven't suffered.
If your budget stretches to it, would go for a balcony. If you've more than 2 people in a cabin, it will either be pullmans (they drop down from the ceiling) or a sofa bed. Someone commented that the sofa beds block access to the balcony but it's never stopped us using it (we still managed to get out on the balcony) - it does stop you from opening the fridge though!!
Ports: Bergen & Stavanger are the larger of the ports. Very picturesque and lots to see. (if you are into Gardens / photography can recommend visiting Flor og Faere from Stavanger - cruise ships usually call this the Tropical Gardens of Norway). It's a little island a boat ride away and they plant the island up each year and it's a stunning floral display. You would usually need to book via a ships excursion as the timings don't work usually out to book privately.
Flam - stunning scenery. Can take the Flamsbana train (can book yourself or via cruise ship). Just make sure you're back in time to catch the ship!
Geiranger - small town at the end of a very pretty fjord. Make sure you are up on deck 45 mins before arrival as you pass the Seven Sisters and "Johnnie Walker" waterfalls. Another waterfall in town with path you can walk up to the Visitor Centre. You can also do a trip up Mt Dalsnibba. If clear day you get stunning views over the fjord. When we went, we left Geiranger in brilliant sunshine ... at the top of Mt Dalsnibba we encountered blizzard conditions and could barely see the rails let alone any view (this was early June!!). The chap wearing shorts and flip flops didn't get off the coach! We did get stunning views on the way up.
Olden - tiny town, very pretty. Trips to walk to the Brikdal Glacier or the Loen view point
Andalsnes - small town - trip to the top of the Trollroad
Alesund - large town with fantastic architecture. If you've kids, recommend the Aquarium. Can get bus or taxi there - far cheaper than ships trip. Can climb the400+ steps to the view point (or get a taxi there and walk back down).
Have fun deciding which Norwegian cruise to book!