Your boy will not get lonely. They are solitary fish and getting them tank mates is for us a lot more than for them. They can be completely content patrolling their homes and chasing away outside invaders. So if you are contemplating tank mates to keep your boy company there is no need. If you want a community for your own enjoyment that is different.
If you still want other fish I will tell you I stopped adding Neons with long-fins as they tend to be nippy unless in a large enough shoal. Unfortunately, a 10 does not allow you for a large enough one. I am setting up my 20 gallon long which has a 30 x 12 footprint so I can have 15+ in hopes they will not harass the short-fin Betta.
I would go, instead, with 6-8 Ember Tetra. They are peaceful and slower moving that the Neons. But you will need at least six for a proper shoal. Keep in mind that you are putting prey fish in with a predator and there is safety in numbers. If you can find Habrosus Cory you could also have six or so of them as they are bottom dwellers. This gives you the Betta as your top-dweller, the Embers in the middle and the Cory on the bottom.
The tank should be well planted with either live or silk plants to break up the Betta's line of sight/chase. And have a back up tank ready or a place to rehome the other fish should your boy prefer being a hermit. ;-)