Thanks for all of your insight everyone! I'm definitely thinking very hard about this and greatly appreciate everyone's input. Only, the more I'm thinking about getting a second, the more I want to get another budgie for me as well
Since Bella is more independent, I'd like to see if I can raise a budgie that is more willing to spend time with me and to build a greater sense of companionship. I am fortunate to have the resources for another one, but I definitely want to put Bella's well being over my own wants so I'm still leaning toward leaving her as a single budgie (maybe even try to get her a larger cage and more resources to keep her entertained) but I'm going to visit a bird shop and just scout out what their budgies are like and hopefully get more opinions on what would be best.
Here are a few things I've noticed about her behavior that make me think that she might like having a bird friend: she always calls to the wild birds outside, and sometimes we'll play budgie noises to see how she reacts to them and she always does one really loud chirp after another as if she's trying to call out to them. She also seems to enjoy people being around her. During the mornings and early afternoon, she likes to hang out with me on my finger/shoulder and look outside the glass window with me. During other times of the day, she doesn't like to be played with, but likes to have people around her and talking to her. Every time I walk away, she would call out for me to come back and just look and give her compliments, but not touch (such a princess, I know). She eats when we eat as a family, and seems to like having company during her meals. Also, she is really affectionate towards her K&H bird heater that we got her off of Amazon. She preens it, sings softly to it, and very rarely even regurgitates food for it. I don't know if this is healthy behavior to show towards an inanimate object, or if this means she might be longing for a friend so please let me know if that's normal or a sign of loneliness.
However, I've also noticed that she can be territorial. While I was wiping down her cage earlier, she showed a little bit of aggression towards the napkin I was holding (she flew into her cage and tried to peck at it once) and she shows similar behavior towards her food bowl when move my hand close to add spinach to it while she's eating. I think she might have a more dominant personality when it comes to her belongings. I'd definitely be prepared to have two if everything if I get her a friend.
Also, if I've read a lot of contradicting material about gender pairings. If I have a dominant female, what do you all think would be the best ideal pairing for her? I've heard females can get along together wonderfully, but others say they can be more territorial and having a male partner (with proper anti-mating precautions) is a better fit. Any thoughts would be greatly appreciated!
Thanks again everyone!