Hello! I am single and have been trying to conceive for some time - I don't have any children, though, so my situation is a bit different.
One observation I would make here is that your post is very focused on the possible impacts on your existing children, and less on the possible impacts of donor conception on any donor-conceived child you might have. So, for example, you're thinking about whether your children would resent a baby getting to spend more time with you - but how might that child feel about their older siblings being able to have a relationship with their father, something a donor-conceived child in this situation probably wouldn't have? Of course, it's perfectly natural (and very sensible and thoughtful and empathetic) to be thinking about the impact on your children, - it's definitely something that needs careful thinking through. I would recommend having some specialist counselling to work through all these thoughts and feelings. You can generally access this through fertility clinics (and, in fact, it's usually a requirement before using donor gametes anyway).
May I ask how old you are? I don't mean to be insensitive, I'm asking more from the point of view of your treatment options and likely odds of success. Were you thinking of formal treatment through a clinic or did you have some other arrangement in mind? It's probably a good idea to take a careful look at your odds of success, and the likely cost implications of treatment, in making a decision. How much could you afford to spend on treatment, and how will you feel of you aren't successful? Practically, if the best treatment for you turns out to be something more complex like IVF, is this workable for you?
I'm not asking those questions to put you off, at all. I am on this road too, after all - so clearly it's something I consider both possible and worth pursuing. I'm more asking because, I've been on this road for quite a while (4 or 5 years, at this point) so I guess I see it from the perspective of, it's not always easy. And I do think it's important to think about that side of things, and about good self-care, as you decide what you'd like to do.
Best wishes to you and your family, whatever your choice!