If you check out the link I gave, scroll down to where it talks about being desperate for foster homes for cats and kittens.
I am sure that if you could (as an experienced person) foster a mother cat and kittens they would be VERY glad of your help - and if you end up keeping one of the kittens I am sure that would be fine.
Charities are desperate for help from knowledgeable people like you, and often they will pay for all the feed etc. for the cats/kittens all you need to give is love, cuddles and have the space, at this time of year they have more cats/kittens than they can possibly take in and are very glad to hear from anyone who can offer any help at all.
To be honest there is no way I would waste money buying a kitten, far better to approach one of the charities in your area and offer to take a kitten/cat.