You'll be fine. A lot of seasickness is all in the mind (so they say) and if you are out on deck and excited in what's happening, you won't even think of it. The only things that might be a bit iffy are a) putting your head down to read and b) sitting at the front of the ship when it is pitching a bit (Not sure about the Cloud but often the theatre is at the front (bow end) which means it can be a bit bumpy if the seas are rough). Ponant's theatre was at the stern.
You'll be busy on the first two days with briefings and lectures etc and then you'll be at Antarctica!
Anyway it might be smooth - the Drake Lake for you.
One thing to tell MrFM is not to spend all his time taking photos - yes, they are great but sometimes it is more important to just sit and take in the atmosphere of the place (a bit like visiting the Mona Lisa - everyone is jostling to take a photo and no one is really looking at the painting). It is amazing.