Your Will is not the document in which to leave instructions about your funeral or memorial service if you have specific wishes with respect to the same. As a general rule, no one will look at your Will until well after the funeral or memorial service.
The best place to leave instructions for your funeral or memorial service is a Health Care Directive or a letter to your loved ones. Neither of these options will be legally enforceable, but if you talk to your loved ones about your desires, there is a good chance they will try to carry out your wishes.
If you feel strongly about these issues, an option that is more likely to carry out your wishes is to purchase a pre-paid funeral and make the arrangements yourself with the funeral home.