Since you are still having symptoms, I'd guess that 1 grain of Armour will not be too much for you.
When I switched over, I was still fatigues, achy, etc. and I stopped the synthroid (and Cytomel) one day and took the Armour the next. One thing I would do differently would be to take the Armour in 2 doses--split the pill. Take 1/2 a grain in the early morning and then take the other 1/2 grain after lunch. If I had known this, I wouldn't have been so tired in the afternoons for the first month.
This will also let your system get used to the dose of T3 that you haven't had. Sometimes it can hit people pretty hard and cause a racing heart and the jitters for a bit. By splitting the dose, you avoid these side effects. Also T3 is very short acting and only lasts about 6 hours so you really need it twice a day.
I expect that you will feel better in about 2-3 days and continue for a couple of weeks. I found that I crashed and got all my symptoms back in one day when I needed an increase in dose. I had to increase about 1/4 grain every two weeks for a couple of months. I hope your doctor will let you do this too.
I'm so glad you finally get a chance to try Armour. I hope you love it as much as I do.