Thanks Mike and MTL for the feedback. I am picked up from various forums about mid ship and have put that request to my agent today.
At present I have narrowed my options to the Azamara Journey frpm Copenhagen to Copenhagen and the Prisendam from Amsterdam to Greenwich.
I agree you take your chances and it sounds like May/June is ideal but I can only go when I can go.
The other things I have noted in reviews is comments about inside/outside cabins and how HAL should consider blackout curtains.
With the weather I guess all you can do is be prepared with tablets for sea sickness - either ginger tablets or similar.