The best way to narrow down your research interests and figure out what you might like to work on is to get research experience and work with professors. You can start by thinking about what you really enjoy in class. Have you taken intro to sociology and some basic sociology major courses yet? You can also use your college’s library to read some journal articles in sociology. If you don’t know where to start, talk to one of your sociology professors and ask for some recommendations for what to read. They can help you figure out the building blocks of a good foundation in the field, and you can start figuring out what you like.
Since it’s summer, I would wait until it’s closer to the beginning of the school year. Many professors travel over the summer and don’t respond to emails frequently. When August or September rolls around, you can begin to investigate which professors might need a research assistant in their labs.
Research assistantships are also a good way to get to know professors and make close connections. When you do apply for a PhD in sociology, you want at least one of your letters to come from a professor who has supervised you in research. In lecture halls, one of the ways to pursue a relationship is to go to office hours. It helps if you are genuinely interested in the material; then you can visit office hours and talk to the professor about them. You don’t have to form relationships with EVERY professor you take a class with; save it for the ones whose classes and research you really like. If you go to a large research university, you can also form relationships with the grad student TAs and maybe some postdocs and that may facilitate getting into a lab. (A lot of times, the grad students and postdocs recruit and select the RAs in the lab.)
Heavy quantitative work and computer science are really good skills to pair with sociology. More and more, the social sciences are requiring computation and quantitative skills to do certain kinds of analyses, and if you have the skills you’ll be in higher demand and more competitive for jobs. Check out, for example, Stanford’s Center for Computational Social Science: https://iriss.stanford.edu/css. The University of Chicago has a master’s program in it. And I know you’re a sociology major, but psychology has an entire field of inquiry that’s about developing mathematical and computational models for doing psychological research - it’s called quantitative psychology.
As someone interested in the social sciences and computer science, you might also be interested in human-computer interaction, or HCI. You also might be interested in something like decision sciences, like this PhD program at Carnegie Mellon: https://www.cmu.edu/dietrich/sds/graduate/index.html. Another good fit field is information science (you can see UW’s information science research areas here: https://ischool.uw.edu/research/areas). Sometimes this field is called informatics. Many business schools also have programs that are more quantitative in nature, but grounded in the social sciences.
As it seems like you know, academia is a tight job market. It’s very difficult to get a job as a tenure-track professor in sociology these days. Most people who get a PhD in sociology actually won’t get one. The good news is that there are quite a lot of things a sociologist can do other than academia. With an interest in CS as well, an easy path is human-computer interaction or user experience research. Many tech companies hire social scientists to do this work to help them shape their products and services for human use. (This is what I do!) Other options could be market research, social science research at think tanks and NGOs, strategy/management consulting, and lots of other positions in business. The unemployment rate for PhDs is very low, and as long as you pursue internships and other opportunities in grad school to keep your options open you should be fine.
Don’t rule out pursuing a career in business, particularly if you have never tried it. My PhD is in public health and social psychology, and I never seriously considered working in a for-profit company with it - I was interested in diversity and social justice, and thought that the public sector was the best place to take my talents for change. But I’ve been able to make a great impact at my company in the private sector with my expertise.