Outside of TT, the IOM is like any other tourist destination. You can book a package holiday or you can book your travel and accommodation yourself separately.

The Steam Packet will tailor make a holiday for you if you prefer.

Alternatively you can view all the accommodation via the IOM Government controlled website and book it directly https://www.visitisleofman.com/

I see no real advantage in either way and as a personal preference I like to do all my own bookings.