If I were you, I'd narrow down more of the criteria you want in a trail horse. There are actually a lot more things that I believe are important to know about a trail horse than just "not spooky" and "will go out alone."
What is your preferred pace? Do you want a horse that is very comfortable, or is it more important that the horse can get somewhere? I know many horses that are not spooky and will go out alone very well.
Some of these horses prefer to only walk slowly, must be really pushed to maintain a slow pace at the trot, and are best for very slow and sleepy rides. If you wanted to cover, for instance, ten miles on your ride, it would take you several hours or more and you'd have to prod the horse quite a bit and wear yourself out to get there.
Some other horses I know are medium paced horses. They will walk, trot or lope but they don't have the drive to go all day without pushing. These types can take you on a short trail ride very well, and keep up with many other companions you might find to ride with. But if you want to do any rides farther than about ten miles, you'll find them lacking. They will not ever place in an endurance ride.
Then there are some other horses that are not hot, but move out at a very good pace. They can trot for miles, it's very smooth and you will cover a lot of ground. Some gaited horses such as Tennessee Walkers fall into this trail pace. If you want to go out and see a lot of countryside, you'll be able to do it. They might not win an endurance race, but they could easily finish it once conditioned.
I won't mention the horses beyond this that will take you fast, all day since you don't want a hot horse.
Looking at horses, I'd keep in mind the type of trail riding you want to do. If you're going to need a horse that can scramble up steep slopes and get over big logs in the path, bear that in mind. If you want to walk slowly on groomed trails, your very stocky QH or Fjord pony (in your example) would do. If you want to go farther distances and do more trotting out, I'd get a bit leaner looking stock horse that is not too heavily muscled and will handle distance and heat better. It's not just about temperament to handle spooking and obstacles, but also the horse must have the drive to work and the physical capability to handle what you are asking.