Correct usage of the word "lack"

I was writing an email yesterday which was about a rough draft of doc to be reviewed by a peer. There was just one part of the document which I thought needed improvisation.

What I wrote is → "The only lack I feel is …."

After I sent the email, I realized the same sentence could have been framed better like this → "The only thing lacking in my perspective …"

Although I try to avoid using the word "thing" within formal emails, I felt in this particular scenario, using the word "thing" would suit the purpose.

Would someone kindly appraise me if the sentence which I framed, "The only lack I feel is …." is grammatically correct or not?

Also, is the second sentence "The only thing lacking in my perspective …" a correct fit to put forth my idea, or can it be framed better?

Any suggestions would be gratefully reciprocated _ / _