Hi Shell,
I worked on Jersey for a year and I took the ferry from France half the time and flights the other half the time. In the end I wound up taking the ferry with my bike and cycling into work because work was a 2.5 minute cycle from the port.
I have a question. Are you going to a hotel? If you are going to a hotel you would need to make sure they have parking, I tried having my car there for the first month and gave up as it sat in the car park and cost me a small fortune to keep it there. If you are going to cottage let or something like that then parking won't be an issue.
Locals to Jersey have vehicles but people arriving with them are really not encouraged. For instance if you want to bring a caravan you have to have a site booked before hand.
The Condor Ferries is a Sea Cat. High speed catamaran but it is not huge like the HSS which go between Europe and the UK. It is a reasonable size and you can wander around a bit, but it is nothing like the size of a cross channel ferry.
https://www.condorferries.co.uk/remote.axd/condorlivemedia.azureedge.net/media/3025/liberation-map.pngThe first time I went over was from Poole. The journey was fine but then I don't get sea sick I'm not claustrophobic and I don't get bothered by sick people around me. So I'm probably not the best judge as to the comfort levels.