Verticals of quarter wave or less height are not considered balanced
(like a dipole is), unless you have at least two radials as you have.
In fact the original prototype ground plane by RCA had two radials, but
the salesmen thought three or four would look more symmetrical to
customers, and that was the way production wanted the ground plane
But, for your case and many others; yes, you could use ladder line to
feed it and even transition to 300 ohm balanced line to enter the coax
plug, so that you can use the coax jack.
Les Moxon. in his RSGB England book, "HF Antennas for all Locations"
shows ladder line fed quarter wave verticals as you describe. This book
is available from ARRL and other radio booksellers.
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