Would it be advisable for me to get another cat?

I have an approximately 7 year old female rescue cat that I got about six years ago. She is spayed but still has her claws (I disagree with the practice of declawing cats.) She used to be really bad with new people (like anyone other then me and my boyfriend) and even worse with other animals, but now she's a lot better (with people, at least). She absolutely hates to be held (by anyone) but will almost always come when I call her and likes to snuggle with me in bed.

The problem is lately, if I leave the apartment for more then a couple of hours, she is absolutely frantic when I come home and won't leave me alone for at least an hour. I'll find new claw marks on all my furniture and her food dish will be completely empty (like, she eats way more then she does when I'm here.) One time I was on Skype with my boyfriend and went down to the corner store. When I got back, he told me he could hear her whining the entire time I was gone (like, 15 minutes, max).

I don't know if this is just normal behavior for a rescue cat, but to me, she seems lonely. I am considering getting another cat, to help keep her company. But the problem, of course, is that she's not so great with other animals. Personally, I think if I get a kitten (as opposed to a full grown cat), my cat's motherly instincts would kick in and she would like, adopt it, especially since she's never had a litter of her own. I would also get like, a pet tent to safely introduce them to each other. My boyfriend says that since she's a rescue cat, she'll just see the new cat as a threat and treat her as such.

However, a couple of years ago, we brought her with us to my boyfriend's parent's house and they had two cats at the time (a male and a female.) After about a week, my cat was less aggressive with the other female, even sniffing each other and playing a little. I think if we had stayed for another week, they would have become pals. Also, my parents have a half shih tzu half bichon frise (a female that is just about the same size as my cat) that my mom occasionally brings over to my apartment. The last few times she's been over, my cat hasn't growled at her at all. The last time they were over, my mom's dog went straight for the food dish and my cat just sat there and watched her, not complaining at all.

I think she'd be all right, but I don't want to find out the hard way that she won't. I'd really like the opinion of a veteran pet owner or an animal expert. Since this is kind of a serious request, please don't post unless you really know what you're talking about. Thank you for reading.