First, congratulations on deciding to transition to consulting. It's a challenging yet rewarding field, and I'm sure your research experience will serve you well.
Regarding the employment gap, it can raise questions, but it's not an insurmountable issue. Here's how you can handle it:
Be prepared to explain the gap: If asked about the gap in interviews, it's important to provide a clear and reasonable explanation. You mentioned that you spent several months thinking about what you wanted to do next. Frame this positively as a period of self-reflection, career exploration, and skill development. If you took any online courses or attended workshops related to consulting during this time, make sure to mention them.
Freelance work: If you worked on research projects for your former employer during this period, even without pay, you can definitely include this on your resume. Instead of extending your work history for the same position, you can list it as a separate consulting or freelance research role, indicating that you provided services voluntarily. Ensure that you highlight any transferable skills or achievements from this period relevant to the consulting role you're applying for.
Remember, the aim is to present the employment gap not as a period of inactivity but as a time when you were proactively preparing for your next career move. And it's great that your former boss is supportive; references who can vouch for your skills and work ethic are invaluable.