Replying to Question about Atomic boot flex

So the local boot shop fucked up my boot fit. I complained and they're going to replace my boot. The original boot was an Atomic Hawx Ultra 130. One of them feels great and I'm certain that with the right fitting they're the perfect boots for me.
Only problem is, is that the shop and supplier have run out of 130's. I'm in Japan so it would probably take a while to get a pair of 130's in. They've offered me the 120 but I'm unsure if it will be stiff enough. Would a stiff booster strap make if feel like a 130? I ski aggressively on all terrain and weigh 71 kg's so am pretty doubtful the 120 will give me what I need. This is the first 2 piece boot I've had in years so I don't have much reference of flex differences. Before was wearing the full tilt Seth which is stiffer and more supportive than people tend to think. Any help is much appreciated!