Hi SwanOrnament,
I'm sorry it's been so hard for you for so long. Coping with BPD behaviors can really wear a person down -- I know

That's good that you are ready to get some help and support for yourself, and that you're being proactive about thinking about what kind of counselor you'd like.
Logistically, you can decide if you would rather see someone in person, or remotely (Zoom/video chat). I prefer meeting in person so someone who only works remotely would be a No for me -- but might be a Yes for someone else (convenience, no driving, etc).
My insurance does not cover my counselor, and that can be a big factor in decision making. I use a HSA for payments (health savings account) so it doesn't come out of my bank account. You may find a great fit with someone who is out of network, and if so, you can talk to that person about "cash payment discounts" or other payment plans. My counselor does have a sliding scale.
In terms of the counselor's expertise, you can ask directly if s/he has experience with personality disorders and/or family dynamics. Even a counselor who specializes in working directly with pwBPD (via DBT or other modalities) may be a good fit for you, because of knowing what pwBPD are like.
You are allowed to meet with the counselor and then decide if s/he is a good fit for you. You aren't required to keep seeing a counselor with whom you don't "click". I met with a new counselor once and she talked about herself too much for me -- I didn't go back. That's fine.
For me, the relationship with my individual counselor has been more important than her specific expertise. Because I feel like I can trust my counselor and that she understands me, I can do a lot of work from there, even though she never advertised that she has experience with PDs. It took me a year or two to share my suspicions with her (about my H's kids' mom and stepdad) and she definitely understood. I think many or most counselors, regardless of what specialty they may go into, likely receive some training/education on family dynamics and PDs in their schooling.
I think sharing with any potential counselors just what you shared here:
To say I’m not feeling too good is an understatement and relies I need to look to a counsellor for assistance. What qualification, attributes do I need to look for in order for this to hopefully help me become more assertive, resilient with boundaries and how to start taking care of my emotional wellbeing ?
would be a great help -- even if the potential counselor doesn't work in those areas, s/he could refer you to someone who does.
Let us know how your search goes. We're rooting for you and your wellness,
kells76