Hello! So, here are some rambling thoughts from someone in a somewhat similar position...
In terms of 'selfishness', I'd say parenting is ultimately one of the most unselfish things you can do, and if you decide to go ahead I don't see that there's anything selfish about doing so. If you were in a relationship and wanted to start a family, would anyone call you selfish for that? No, they wouldn't. And it sounds as though you have given this some thought, done the maths, and have a credible plan for how this might all work. That also speaks to a degree of care and thoughtfulness that's anything but selfish.
I started trying to conceive on my own when I was, oooh, 38, I think? Might have been 37. I am now 42 and haven't yet had a baby. So, on the one hand, I do think there's merit in not leaving things too late. On the other hand, at 34 I do think you have some time to play with. It's not so much a cliff-edge at 35 as a gradual drop off.
If I were you, I'd go to a fertility clinic and get a full work up done to check things like whether you're ovulating, whether your tubes are clear, whether there are any indications that your ovarian reserve might be low. Basically, get some information, as this will help you to make decisions.
One question I'd have for you is, would you be open to seeking to become a parent in the context of a relationship? Clearly, I don't have any issue with the answer being 'no' here, but I'm conscious that for me, part of the reason I decided not to go all out looking for Mr Right was time - even if he'd fallen from the sky the instant I started thinking about starting a family, I would clearly have wanted some time in that relationship first and that just seemed too pressured. (The other reason was, the more I thought about it, the less bothered I was about the idea of a relationship anyway.) But I'd say that at your age, you do have some time to seek that out, if it's something you want (and assuming this would be a relationship with someone with sperm).
So, yeah, my tentative suggestion would be to get some tests done and then, armed with that information, have a good think about how you might like to proceed. Good luck, whatever you choose!