Hi Rhys,
Your maintenance schedule looks good.
Historically, changing from one motor oil brand to another should not cause any
problems, either.
I know what you mean about becoming a father. I seemed to have all the time in the world before I became one and then........
Kids grow up quickly, so if I were you I would cherish the time with her as well.
You say that you have a trusted garage that you have used for years.
If that is the case, I would get them to have a look at the car and see what they diagnose.
It might be an inexpensive fix, or, on the other hand, expensive.
As least it would give you a better idea of where you stand.