Generally, you will have no issues with getting endometriosis life insurance and most cases will be offered at standard rates (the same premium as someone with no medical issues).
The only instance where your cover may be more expensive or may even be declined is if you have other health issues that can cause issues for your endometriosis such as high BMI, diabetes or other issues.
As long as your condition is stable, and you have no medical investigations as a result of your endometriosis then your application should be accepted without a medical report.
As a whole, endometriosis is classed as a mild condition by insurers and generally you will have no issues with getting cover, it is very rare that you will be declined cover unless your condition is extremely severe or you have other medical issues as a result of your endometriosis.
As long as your condition is stable, with or without medication, you are not under any medical investigations and you do not have any other medical conditions then you should be able to get cover without any issues.