Pitchounette, I've had another think about your son's difficulties, which you said in your OP were mostly about blending.
Have a look at the following books. They are designed for the youngest readers OR those with severe reading difficulties. The Alphabet Code is taught in context of the words and is done through an extremely slow progression, hence the huge number of books.
The reading needs to be done at first with a 'slider card' so that only one grapheme is revealed at a time -to avoid whole word memorisation, which is a danger with this style of phonic programme. Your son would get a huge amount of blending practice with this programme.
www.marriottmd.com/sam/index.html
If you're interested in learning more then you can get all the book sets / info. on making a slider card and research etc. here:
www.piperbooks.co.uk/index.htm
There's also a Yahoo support group for the programme, though you'll need to register to join: [email protected]