Depends on a few of things: the size of the variables and your CPU architecture.
What does sizeof(double) return on your system?
What is your system?
Most likely if you're using a fairly modern 32-bit PC, all the above code will be small enough to fit in cached memory, maybe even the L1 cache, so it'll just be doing a simple register compare which it can do in a single instruction, just as it would for int, bool etc. Probably those who told you double would be more expensive were brought up on ZX81's and forgot things have progressed a bit since then.
The key really is to run a test and see what performs quickly and what doesn't within a relevant scenario. In general yes a double comparison could be slower than other comparisons and double arithmetic could be slower than other types, but the main thing is to profile the code and see where the real slowdowns are.