Equivalencies aren’t exact, but based on your previous history with 60-70 mg. of Vyvanse, your dosage of for Adderall (or it’s generic) should be 30-40 mg a day. As you’ve noticed, the problem with Adderall is that it has a shorter window of effectiveness. See if doctor will prescribe 30 or mg per day but as 90 or 120 10 mg. tablets, or maybe 60 20 mg. tablets, so you can cut them easily. Then try a first dose of say 20 mg. when you normally take it and a dose of 10 mg. around 2:30. Or even dosages of 15-20 mg each. You get the idea: you just have to play with it! I’m afraid it will, however, take twice daily dosing.
I know this is a PITA, but I do have some idea what you’re going through. I had to do this year’s ago with Concerta, not because Concerta wouldn’t work for me, but because doctor wouldn’t prescribe high enough dosage, so I had to get generic Ritalin (still in an inadequate total dosage) and decide how much to take when to cover what situation…work, school, home. Luckily, your dosage requirement doesn’t seem excessive, so it should be just a matter of playing around with it. In my case, it was trying to make inadequate dosing work in my life: it didn’t.