"completely personal" is correct and can be used in written English.
For example, "My decision to move to a new city was completely personal."
"My decision to resign was completely personal.
Passionate and prejudiced, Cobbett's prose, full of telling phrases and inspired ridicule, was completely personal.
Later he developed a completely personal style within the Cubist tradition.
Most artistic enterprises are completely personal: the work of one individual, with an idea.
The idea is that it's completely personal and unique to you".
The men at Restrepo seemed to make "sense" of combat in a completely personal way.
The team lost only two matches during the tour, with Wisden saying, "No travelling team ever strove harder for victory or more completely subordinated all personal considerations to the prime object of winning matches.
Some apps can give you full control of your phone should it be stolen, allowing you to track its location or even completely wiping all personal data stored on the phone.
If they were on the brink of getting a loan it was only if they completely gave up all personal guarantees and signed over everything to collatorise it.
You'll see a beautiful reflection of yourself, a visualization of your life crafted by an artist, ever-changing, totally personal, and completely unique, just like you".
It really is completely a personal situation.
