Hi welcome to the site,
I would say setting boundaries is an essential part of self care. People with BPD are experts to convicting us we should not have boundaries, primarily because it prevents them getting what they want, and they don't really consider other peoples boundaries at all.
Your point about doing it in a loving way, be aware a BPD does not like boundaries so will throw everything they have at pulling them down. I know that’s what shocked me when I began the process, but if your BPD has had things all their own way, why on earth would they want to change anything that suits them first ? BPD is more likely to consider you as week if you allow them to take advantage.
There are various techniques on this website to minimise the fall out and to make the process easier. Techniques such as B.I.F.F. or S.E.T. But briefly put, you need to be firm but fair, knowing your BPD will try and convince you are not being fair regardless. Here’s a link to more detail:
https://bpdfamily.com/content/setting-boundariesI hope that helps, but you may find this is an incremental thing, where getting feedback from this forum after trying various thing may help. In that we BPD children have been taught to allow our BPD total and unvented access. For example, my BPD use to listen in to all our phone calls and steam open letters. One of my siblings, still to this day thinks that’s OK and does the same with her kids. I think you will find this forum would correctly point out that is not OK and is in fact its illegal in my country. So if you want council on what is "fair" or back up when things get rocky, feel free to post on this forum.