Shortest overwater crossing is from St Bees Head, but it's a long way up to there and extends the total route considerably.
I have flown to IOM from Barton, Liverpool, and Blackpool when I was lot younger. I actually wouldn't do it today in a single as I'm a tad more circumspect these days and always like to have an 'out' when flying. Engine failure is a vanishingly rare probability, but it could happen and if it does over the Irish Sea survival is unlikely.
However, lots and lots of pilots make the crossing every year in singles and few have persished, so I'm not saying you should share my view.
Enjoy the flight.