It’s great you are managing to improvise well and still practice serves at home! To be honest with you your adaptation sounds good, especially if you are more comfortable with it and can generate spin easier. The body rotation you mentioned is key with these backhand serves and makes sure you can be relaxed in the arm and wrist and also recover to the right position. To really get pure backspin on backhand serves isn’t that easy and a little bit of side spin usually will be there.
With the serve toss it has to be near vertical to be legal so I would be slight careful if it’s going to 45 degrees, just try o get it as straight as possible.
