Thank you for the clarification that the 6'0" is not available for you to use. But what is not clear now is your Dad wants you to use a 5'4" or 5'5", but you countered his advice with maybe wanting a 5'6" or 5'7". And to top that you threw in 5'8" or 5'9".
Since you've used Firewires before, I used their volume calculator to see what size board is recommended for you.
This shows boards of 20-24 liters in volume with sizing ranging from 5'2" to 5'4" for 23 liters.
BUT............. that is if you are an INTERMEDIATE surfer.
This shows boards of 35-43 liters in volume with sizing ranging from 5'10" to 6'2" for the lower end of the scale at 35 liters for Beginner surfers ( usually those who can't turn or cutback ).
YOU need to figure your true level of surfing. You need to rely more on YOU, not the board.
We can not answer or give you advise if you yourself are confused. You need to try a 5'4', 5'5",5'6", 5'7", 5'8" or 5'9" to see if you can actually surf it. And if there aren't any boards like that to try, then take your best quess-timation and live and learn.