I've realised that anything wheat based causes me bloating, gas and stomach pain.
Christmas will be a struggle, our Christmas day breakfast is usually brioche and croissants, what can I have instead?

Welcome lamberta,
Good that you have recognized that grains cause digestive issues, it's always easier to pass on an item when you know it causes distress. And you are already following the book and diet I recommend when sugar and grains need to go...it is the simplest and easiest to follow. Eat only what is on the permitted list of foods until at goal weight. Eat only when hungry, stop when full.

Gary Taubes is a great science journalist, but the Diet he has in his book is the plan used at the Duke Lifestyle Clinic by Dr Eric Westman, and the one I follow. You can find much more about it on the DietDoctor website too, his two week Keto challenge is based on Dr Westman's No Sugar, No Starch plan. https://www.dietdoctor.com/low-carb. Here is one of Dr Westman's talks..it is not just diabetes but obesity too.

As for Christmas you can have a filling egg casserole with sausage , bacon, veg. Make it up the night before and pop in the oven when want to serve it. If you want to get into wheat-free baking, there are alternate flours (almond, coconut, Flax) look in the kitchen forum here or on the DietDoctor Recipe section for breakfast/brunch ideas. https://www.dietdoctor.com/low-carb/recipes/breakfasts
Another recipe blogger with YouTube instructions who uses the Dr Westman Diet and keeps carbs to 7 per meal is Kristie Sullivan, http://forum.lowcarber.org/showthread.php?t=470795
This NZ recipe blogger uses coconut flour more than almond...many ideas for recipes if you want to make a special bread substitute for holidays. https://www.ditchthecarbs.com
All the best

Ps: you live in a lovely county! I lived in London for about five years and would explore the Home Counties on weekends. Add some walking if you don’t already enjoy the paths around you.