Yes please be aware that the proximity of the two can also stress them both unless you put something up in front of the divider to keep them from being able to see each other constantly. Bettas do not get lonely, they are used to being alone and if you feel they must have another fish with them it really should not be another antabanoid (betta, gourami) or semi-aggressive fish (shark, barb, danio, angelfish). They are also not good with tetras of any type but the Cardinal Tetra. (Tetras are fin nippers and will eat your bettas fins)
They ARE compatible with Cories, Catfish (Otocinclus), and Loaches that I know of as those are the ones that they get along famously with in my tanks. They also get along well with Plecos because the Plecos are night time fish and they never see them but for your size tank a Pleco is out of the question. I think they would get along with Rasboras or White Clouds but it does depend on the betta.
When you add fish to a betta tank ALWAYS be prepared to remove the fish if a problem occurs. Every betta is different and some of them will NOT tolerate ANY other fish in THEIR water. I have had bettas who accepted tankmates who really were the problem makers and caused the tank upsets and then I have had bettas who killed everything I put in with them until I just gave up and let them have the tank to themselves. Every betta will determine his or her own likes and dislikes and there is no way of knowing ahead of time so this is why if you insist on trying the addition of others, you have to have a backup plan or you may find yourself with war in your tank and be frantic. You WILL have war at some point and some dead fish if you mix two bettas or gouramis with bettas or some of the semi-aggressive fish with bettas. This is not a scary story that I am telling you to scare you, it will happen. If you read far enough back in this very forum, you will find examples of people who decided to give it a try anyway and had disaster after disaster.
As I have said before I cannot make up another person's mind for them, but I would be not doing what I am here for if I did not point out the dangers involved with some of the combinations.
Rose
