You might not need to do it with a "mud base" as some call it, or a "mud job". You might be better off using cement board. Please describe what the floor is below your mud base, ie: plywood, 1x boards, and what condition it is in, and how much you need to raise the base by to make your tile flush to the surrounding finish floor, and whether you need to accomplish any leveling, or can you just raise it the same throughout the area. We really need to know the condition of the sub floor- is it creaking? how solid is it, what's it made of and how is it attached to joists. If you answer ALL of my questions then we can give you some good opinions.