Yes, 10m to 12m will be right for you if you only have one kite in Perth. I use an 11m and am between 90 and 100kgs depending on how full the fridge is.
Be very wary of instructors that take you out and they weigh 30kgs less than you! It is a big difference and a lot of instructors don't understand this because they have only ever been whatever they are.
Of note I had a French guy that looked to be all of 50kgs giving me a lesson on the river and I weigh double that

He couldn't understand why I couldn't just 'park and ride' and why I was just sining the kite all the time to keep going. Another intructor refused to let me use the 14m kite on a light day even though he was about 20kgs lighter and was just barely going.
Don't put up with it, as it will delay your progress a lot! This does make it difficult for lighter instructors as to them a 14m will be over powered in the same conditions where you think its okay. Unfortunately until you get your technique sorted out, you do need that power and less is going to make it much harder to get the waterstarts nailed. Try to find someone closer to your weight as an instructor as it really does change things.
While I agree with Christian that a lot of windsurfers have that reaction of pulling in the bar, I did too, its not that hard to overcome it.
I was also surprised when another learner was telling me 'there is no overlap between kiting and windsurfing'. IMO absolute BS. Once you understand the wind, there is a lot of overlap.
Don't do what I did either and just do lessons here and there. I did lessons to fill in time each season and didn't progress. When I finally comitted to going out by myself, I went from very poor waterstarts to easily going up wind within a week or two. The rest is finesse.
I also warn you of getting the right board. The nice big floaty ones they use at Safety Bay for lessons are awesome for a beginner as they plane easy and get going in lighter wind. My first shop bought board is a 145cm (a tronic) and it is crap as the overall surface area is not enough, yet a board I bought later (a CBL) is supposedly the same length (well 144), but has more surface area and goes a lot lot better. (Wanna buy a Tronic... it would be perfect for you ;-) )
I also have a home made board of about 155cm and wide. it gets me going in light wind without needing to change the kite, and its worth its weight in gold.
I should offer myself to the kite schools as a sea-anchor to hold down the big kites for people like me

but joking aside, if you get a lesson from an instructor that cannot use the same size kite as you, it will hold back your progress.