Also gay couple, 17w with first child.
We considered brother, friend, gay coparents etc. and signed up for the coparent web site but decided in the end that we wanted it to be clearly just two parents, so we went for ivf with an anonymous donor.
Ivf because insemination takes so long and ivf is free where we live.
Tips:
Our friends had 18 tries with both mothers trying because where they lived they don't do investigation until after 5 unsuccessful attempts per woman, which is a lot of cash. We had hormones, clotting factors and tubes checked first so knew that one tube was blocked, so saved ourselves from literally spunking away half our cash on insemination. Id don't know what the nhs will do for you but you might want to see.
If you use a known donor, our clinic told us that there is only a 10% chance that their sperm will be perfect. This was also a factor for us in finally deciding to use an anonymous donor.
If you use a donor, make sure you can reserve samples for a second child if you think you might want to. We have 30ish straws for child number two.
I've read that inseminating at home with frozen sperm from a bank is very hit and miss. You might want to reseach the success rates between this and clinics and see what you think.
There is no best route, just the one that is best for you both.
As the non-gestational mother of number 1 (I'm having number 2) I was surprised how extremely attached I feel to the baby, and I think this is because the donor is anonymous and because I arranged all the clinic stuff. I really feel that I got her pregnant somehow because I was so involved, although actually it was another woman, a very nice doctor, who got her pregnant.
We went to a clinic that advertises a lot to the gay community and has a special web site for lesbians. I didn't want to feel like an exception to the rul during the treatment. It's nice because there are always other lesbians in the waiting room and at the information evenings.