Nursery vouchers from the government only apply to children over 3, I believe. Or are you referring to vouchers from your employer?
Tax credits will pay you an amount of 80% of your actual cost up to a certain amount (£140 pw) and your entitlement will depend on your earnings.
The HMRC website is pretty good, although they don't always answer all your questions easily!
Childminders can be more flexible than nurseries, eg once every few weeks I would have to attend an evening meeting so my lady had them till 8pm; and are probably better for 1-to-1 with babies - although some of them try to charge quite a bit more than nursery rates. But you really have to visit any nursery and childminder to decide if they are going to provide the service you want - went to trial one seemed nice and professional, but in her home she had the tv on the news channel, no toys out, and stinky dog-hair everywhere.
I would also seriously look again at your outgoings and how necessary they are - you will really miss out if your little boy goes full-time. I worked out that I was only earning £50 a week extra after childcare/travel etc, so chose to leave that job after being back a little while, and earn the extra working from home instead. I dumped cable tv etc (£50 a month) and have just got rid of the car - aaargh - saving another £150 a month but realised I don't need it that much, just got used to it! OH never learned to drive anyway.
x