OK, I am a FTWOHM.
But I fantasise about holidays alone. Activity holidays - a yoga trip to somewhere like Greece, sailing with a group, possibly taking a cruise, certainly doing a walking holiday (probably alone but possibly as a group thing).
If you want a holiday and are alone, think about where you really want to go, what you really want to do, and how much you want to spend.
So you may have single supplements, but you could go on either organized trips entirely, a holiday where you can join in with organized days but have some days to do your own thing, or just plan an itinerary totally solo and see what happens.
What interests you?
Do you want to explore cities, enjoy art galleries and museums, sit drinking coffee/wine while reading interesting books and people watching?
Do you want to do a lot of shopping?
Do you want action - walking (flat or mountains), swimming, sailing, diving, cycling, tennis, yoga?
Do you want to learn something - a cookery course, painting school, writing class, photography sessions?
Do you want to utterly unwind? Spa and a swimming pool with good heathly (and slightly sinful) food? Quiet days with a book and cold drink?
Do you like warm or cold weather?
Do you want to meet people, to make friends or find a partner? Or are you happy being solo (ok - your opening post says not really).
How do you like to travel? Plane, boat, driving, bus, train? Are you happy to mix types, or do a multi-stop holiday (e.g. fly to Paris, couple of train journeys to get to Rome, few days on a boat to Sicily, then plane back home), rent a car/motorbike/motorhome when you arrive somewhere, take a coach tour, or just get somewhere and stay put until the journey home?
Do you want to stay in a hotel, a hostel, camp out, air b'n'b, or guesthouse with a host?
Would you be happy to get a guide for a couple of days to show you what you're interested in somewhere, and build in time (or not) for you to explore or relax solo?
A holiday can mean so many many different things that being alone really doesn't need to mean feeling lonely.