As I am sure you know, IOM airport is extending it’s runway so that regional jets can get in. I would think that the number of services available will increase once this happens.
I know two IOM residents who regularly bounce out of Gatwick for connecting flights and rate it highly.
Flybe to Luton might also work for you too, and London City is also well served.
I personally use Birmingham International, which has the added benefit of being on the motorway and train networks. An under rated airport, with flights to IOM.