I think my grandpa wanted to be cremated
Did he mention this specifically in his dying wishes?
I'm saying that, it's only logical.
While it is good to want to consider your options when dealing with the loss of a loved one you have to consider what they wanted.  It would make you feel better to know that you honored their wishes.
I'm saying I want to be cremated as well. Also what I say goes.
I think that you should follow whatever your grandfather has stated he wanted. This is about them and not you.