I am delighted that dermarolling worked for your face!
We used to sell Tretinoin gel but now we sell Tretinoin cream (0.025%, 0.05% and 0.1%). I am sorry.
Concerning your questions, please read:
https://http://forums.owndoc.com/dermarolling-microneedling/dermarolling-for-thinning-hair/I do not recommend rolling daily with a 1 mm size dermaroller and Minoxidil. You do not have to roll so deeply for Minoxidil penetration enhancement. You should use a 0.5 mm regular dermaroller every other day and a 1 mm roller once a week.
Minoxidil can have quite serious systemic side effects when overdosed and rolling daily with a 1 mm size could result with too much Minoxidil reaching the blood stream.
I used to advice against using > 0.5 mm needles on the scalp because I was concerned/overprotective about the theoretical possibility of the needles damaging the vellus hair follicles but I have extended the size to > 1 mm because in practice it is unlikely that the needles would damage the follicles and a 1 mm dermaroller cannot reach the vellus hair anyway as it penetrates only about 0.7 mm into the skin.
Terminal hair follicles reside about 3 mm deep in the scalp which is too deep for any dermarolling needles to reach. Nevertheless, my concern was the vellus hair follicles that are only about 1 mm deep in the scalp skin and the hair follicles that are in a transitional phase between terminal and vellus forms. Unfortunately, in the process of balding, terminal hair follicles and intermediate hair follicles change and they start growing vellus hairs rather than terminal hair.
Yes, we will consider selling a 0.75 mm size dermaroller. (Meaning, it will be in our store somewhere in the first half of this year).