Seems like this is best answered by trial and error. Write out the numbers from 1 to 100, and, starting from the smallest numbers, pick one and see which numbers are "covered" by choosing that number -- eg if you picked 2 then both 2 and 4 can be found -- and then picking the next smallest number that is missing. And so on. If you don't find a solution then change your choice of (next) smallest number, and so on.
Certainly 1 is needed as there is no other way to cover 1, and also it will become clear quite quickly (I think!) that there can't be a solution using only sixteen numbers that doesn't also use 2. The rest I've not worked through, but I can't see a better approach than this one, building up from the smaller numbers until you have a set that covers every possible number between and including 1 and 100 using the operations given (ie number itself, or double a number, or one number + another).
Good luck. If you still have trouble then I might come back and look at the problem in more detail.