At 105 Kg. ( 231 lbs.) the Go 175 is going to be a bit marginal for volume, unless you have been using
a 170-180 liter board for your 6 hours of lessons.
The Go 175 does not have a centerboard...... did you take your lessons on a board with a centerboard in it?
Something with around 200 liters of volume might make getting from where you are (perhaps not planing
yet?) to fully planing without a centeboard/daggerboard/centerfin significantly easier for you.
If you are already planing on a 180 liter short board without a center board, then yes, the GO 175 (GO 171 for 2011) would be a good choice.
Hope this helps,