Hi timeto. I'm a SMBC. Was in late 30s and finding the sound of the ticking body clock too much pressure for a new relationship, so went the sperm donor route.
Be aware of the timescales - saw my GP in May 2007, had my introductory hospital appointment in August and started IUI treatment in January 2008 (waiting list for sperm donor) but missed ovulation the first month so was the February cycle really. Got pg on first attempt but miscarried, then had another 7 IUI treatments without success which took me to December, then was on another waiting list for IVF which I had in April 2009 - thankfully was successful. DD was born 7 weeks early in November that year.
Using sperm donor is expensive but don't automatically go private, my doctor referred me to NHS and all the initial tests, bloods, clear tubes etc, were free. Then I only had to pay for actual treatment, any failed cycles were free. My IUIs were £650 each time, but that's good preparation for paying for childcare later. IVF was nearer £4,000. If you can afford it, it may be worth going straight for IVF as IUI success rate is very low with donor sperm, but be prepared for 3 IVF attempts.
I had plenty of people willing to be my birth partner, so don't worry about that one.
As for the coping with a child side, it is really, really tough but manageable. Each stage has its issues, cluster feeding and the scratching, pinching, biting phases have been the toughest for me. There will be days when you think you can't cope, but also days that are the best you've ever had and these keep you going.
I don't have any family nearby and the friends I have locally are either still childless and in that not very interested in kids mode or have their own kids and I feel it would put on them too much to ask them to help. Having said that twice when I've had a sickness bug on a weekend, there's been someone able to come over. It would be easier with family nearby, but it's not impossible without.
Be prepared to change your life more than you anticipated. I found it too hard to work full-time and have dropped my hours at work for a year, which has made things very difficult financially, but I love my Mondays with my daughter so its worth it. I also have a day a fortnight when she goes to nursery and I don't work which is great for hair cuts / opticians / catching up on sleep.
Hope that helps. Sorry so long. Check out the Donor Conception Network website for more single mother by choice thoughts and stories.