I would suggest the big Naish 11'6"..You could not go wrong with that board at your size IMO..(you're a big guy at 6'5" and 115kg)
I'm 6'4" and 90kg..I have both 10'6" and 11'6" Naish and use the big board most of the time..It's much more fun..even tho it may not surf quite as good.
I think the 10'6" would be out of the question for you..You could go down to the Starboard 11'2" as a minimum size..The Kalama 11'6" is another option.
The biggest mistake people make is thinking smaller is better and what might be a little difficult now will get easier after time.
You want fun now..not later..and it may not ever get easier..Paddling too small a board for you in choppy conditions is no fun at all.
Which board is right for you also depends on the use..The 11'6" Starboard, big Naish and Kalama are all great allrounders.
The 11'2" Starboard Ultimate Blend and 10'10" Walden and even the new 11' NSP would be great if you're only into waves.
Well that's my two cents worth anyway..

..Where do you live..and have you demo'd boards any yet?
Good luck with it...and welcome.
DJ