Inventing your own pseudo-normalization of Unicode is a worse idea than using the actual normalization forms Unicode defines.

Also, if you think you can decompose without allocating memory... well, try a code point like U+FDFA.

For reference, its decomposition is:

U+0635 U+0644 U+0649 U+0020 U+0627 U+0644 U+0644 U+0647 U+0020 U+0639 U+0644 U+064A U+0647 U+0020 U+0648 U+0633 U+0644 U+0645

(and that doesn't begin to touch any of the potential issues with variant forms, homoglyph attacks, etc.)