First thing to be considered is how big your tank is.
Given the tank is big enough, my thoughts are as follows.
Bettas do not need tank mates.
They are solitary animals and are fine on their own.
The real answer to whether or not a particular betta will get along with this or that (in my experience) is that there's no way of knowing without trying.
Of course, your tank should be big enough to house the betta and any other fish you intend to put in it. The minimum standard is one gallon of water per inch of ADULT fish. There are also temperament issues to consider- aggressive and territorial fish need more space, and plants and decorations to break up lines of sight. Active fish need more lateral swimming space.
Bettas are aggressive and territorial by nature. You should expect them to establish a territory and defend it. The smallest tank I have ever heard of two male bettas being kept in without fighting is a 55 gallon. It can be extrapolated from that, that a male betta could be expected to defend a territory at least as large as 25 gallons.
Female bettas are also very aggressive by nature, and CAN BE just as aggressive as males.
Your worst scenario expectation should be that your betta will be too aggressive to tolerate ANY tank mates. I have had more than one like that, and one was even a female. I've seen shrimp eaten, neons eaten, mollies de-tailed, even a danio isn't fast enough for a betta who means to kick its butt.
That said, bettas can be very much individuals, and some of them can be surprisingly tolerant. I have even seen a few who are positively timid and get picked on by other fish. I had one betta that was buddy-buddy with an African dwarf frog. They liked to hang in the water next to each other.
So, in the end, the only way to know is to try and see.
Be prepared to have to pull out either the betta or the tank mate due to aggression.
My advice regarding other fish is to first try something more innocuous than, say, a platy or any other open-water swimmer. Bettas are more likely to not feel territorial to types of fish that don't really have any territory, like algae eaters (I recommend otocinclus) that hang out on the glass and plants, or cories and other bottom dwellers.
Lastly, the best way to try to stave off aggression on the part of the betta is add the other fish first.
If the betta is already established in the tank, remove him from the tank before adding the new fish. Rearrange the tank so it will look new to him when he goes back in. Keep him out for a few days (a few days in a bowl won't hurt him), and let the newbie/s settle in.
Then, when the betta is returned to the tank, he is introduced to a "new" environment with an established resident. He is less likely to view the whole tank as his territory this way.
