Hi, Alice. I can't speak about ID firms, but I can tell you that many UX firms (including ID firms that do UX project work) and in-house UX teams have design research teams that go by names like "user research" or "UX research." Service design is relatively new in mainstream business practice in the US, but there are more jobs with this description showing up on Indeed these days. In the US right now, it's more likely to be called "Experience Strategy" and they are going to be mid-level to senor positions (not always, however).
You can certainly focus on research. I worked as a designer for 12 years, but then moved over to user research for the past 12 or so — it was a gradual transition. Iab's right: usually in organizations, your work will be focused on either the research side or design side, which means you'll be developing skills in one area more than the other.
1. Read UX/UR blogs and sites. Search terms: "user research recruiting" "UX research jobs." Vimeo has conference talks from UX/UR thought leaders.
2. Get involved with UXPA (User Experience Professionals Association) and IxDA (Interaction Design Association). Both have regional and global annual conferences. IxDA's conference in NYC in February will have a job fair with UX recruiters. Companies like IBM, GE have UX design training programs. Tech companies like Google, Microsoft, Intuit, and Intel hire UX researchers. Firms like Gravity Tank, Frog, Teague, Lextant, Smart, etc. hire people to focus on research, but these are very competitive. It's worth spending money one one good conference to meet people and learn which companies do what.
3. Indeed.com seems to be a good sources to search terms and find companies that are posting jobs in this area. Try a variety of key words. There are many terms for this work. You might approach the company, even the job post isn't a good fit. They might be looking for entry level down the line.
4. Cities that will have more of these jobs include: Boston, Chicago, Atlanta, Austin, Portland (OR), Seattle, Denver/Boulder, San Francisco, New York, Los Angeles.
1. Give yourself a UX research project to do. Need some instruction? Grab a friend and do the d.school's Design Thinking Crash Coure ce (video and instructions are online). BUy "Field Guide to Human Centered Design" from Ideo.org, and walk through the steps in the book to complete a project. That will give you a portfolio piece.
2. General Assembly (several cities) has a short course in user research. Again, complete a project.
3. Read books about design research. And again, find where the UX/UR community is having discussions online. Note where these people work. Medium has interesting discussions and articles right now.