Taking another rabbit in before she’s spayed would just be asking for trouble. You should never put two intact rabbits together, especially hormonal teenagers and it would significantly increase your chances of getting phantom pregnancies, sprays of urine on yourself and the furniture, territorial bitey rabbits and so on… It can come a lot sooner than you think (your rabbit is old enough for all that) and it’s no fun. Trust me, I know.
I know that people often think that babies would get along better but it’s not true : they will get along at first, then hormones will kick in, you’ll have to separate them and begin from scratch again. In the meantime you will risk one of the rabbits getting a serious injury (I’ve seen several cases of a male getting frisky with an unwilling female and ending up getting a castration you didn’t pay for) and / or a female getting pregnant too soon which could end up with a dead doe / a doe killing her babies in a gory way or, in the best case, babies you would have to find families for (some does get pregnant around 12 weeks even though they really shouldn’t).
Especially since you won’t be there to stop them if they fight.
My advice is to wait until your rabbit is around 7 months old, getting her spayed. Then either you take a baby and have to wait one or two months to get him neutered and then 6 weeks to wait the hormones out before attempting to bond, either you take an adult that you can neuter immediatly or adopt an already neutered buck from a shelter.
The best pairing is male / female. It is the easiest, the most stable and I really recommend it if you have no experience with bonding.
But don’t worry, I wouldn’t be that worried about your rabbit being bored,. Rabbits are mostly crepuscular animals and they spend most of the day sleeping – my rabbits litteraly disappear in one of their cardboard “houses” around noon to sleep and I don’t see them again before 6pm. It’s even worse during winter.
PS : really bunnyproof your room before letting the rabbit out. Put hard plastic (the really hard ones or she will eat through them in a minute!) protections on ALL the electrical cords.