Welcome and enjoy your trip.
We were in Ireland a few weeks back and our ferry trip with Stena Line was excellent. We travelled Cairnryan to Belfast, chose the Premier option, priority on and off and a very nice lounge to relax in The food is basically snacks, cake, fruit , cheese n biscuits and white & red wines and soft sodas. The coffee is pretty good.
Our Labrador travelled with us but he stayed in the van, just 2hrs 15 mins so no problems
The costs are pretty high for such a short crossing, we paid return trip £472, but it is what it is !