If you had an autograft using part of your hamstring tendons, then that part of your leg has also undergone quite a hefty trauma. Try using ice on the harvest site as well to try and reduce the swelling as well as elevating your extended leg and doing ankle pumps like you were pumping up a slowly sinking life raft to keep it afloat!
And do not, whatever else you do, get into the "comfy" position with your knee supported with cushions. Sounds like you have been doing that from what you write. It discourages the passive extension, which is really important initially not the flex. I did not have this advice first time around and ended up having to have my knee physically extended under anaesthetic (Manipulation under Anaesthetic). If you want to support the leg, turn the pillows/cushions lengthways and support it from the ankle along the calf. At first it is uncomfortable, but you do quickly get used to it. It also allows you to ice under the knee without putting any pressure on the the area. Once you can do it you can also rest your foot cushions on a stool and literally let the knee hang passively to encourage full extension. I've got so used to it, I still watch TV like that today.
Once you have full extension, you can walk without a limp and the faster you get to this point, the quicker the flex comes back as well.
When do you start physio? If you are still waiting to hear from the NHS there is an excellent guide to general rehab/physio exercises that you could try (under advice from a real qualified person by the way). You will find this in the Information Hub where there is lots of advice about all aspects of ACL surgery and rehab.
Little and often and pace yourself are the best bits of advice I was given! This is a steady long distance jog rather than an explosive sprint of a recovery!