My first post so forgive me if it is in the wrong place or inappropriate 
I have finally conquered pipers grip for the lower octave but find I need to blow so much harder to get the high A and B that the volume is significantly different and just doesnt feel right. Any advice would be appreciated on technique but also recommendations for a whistle which changes octave more readily would be great. I play in a group and change instruments frequently and find the aluminium cold whistle needs warming up which isnt always possible. Tuneable would be good too. My budget for Christmas is about £300. I dont mind used.
Thanks in advance