(background on me so you know where I am coming from: I am 24 and have stage 3/4 endo, adenomyosis and interstitial cystitis. I have had 2 laps and had the coil put in June 2014)
I have tried, and am still on, the endo diet and can honestly say it has made a huge difference for me. This is a link to a brilliant website that is a good introduction and it also talks about vitamin supplements that are beneficial too (http://www.endo-resolved.com/). The author of the website also has a couple of books out (I recommend the latest version) that contain recipes for the endo diet and although they do take a lot of getting used to, I have found it has really improved my pain, fatigue and mental state too. I do still have days where I have some foods on the banned list (chocolate being my main weakness) but I can tell at once that it is no good for me as I get a really achey stomach nearly immediately that goes on to full blown cramps. The endo diet has also hugely improved my endo-related acne.
Like you I really didn't want to go on the coil however, it has honestly been the best decision I have made in terms of my endo. I used to bleed for 3 weeks per month and couldn't leave the house for one of those weeks due to pain and heaviness of flow but I have now got my life back. I am a mature student at uni and have had one day off sick in the last 6 months which wasn't for endo, it was because I had a particularly nasty cold. Before the coil I had 12 weeks off sick in 2013 because of pain and endo related stuff.
If you do try the endo diet and you tend to have a sweet tooth (like me) don't beat yourself up too much if you give in to temptation every once in a while as it is bloody difficult. I always try and have a really good day the next day and have the mantra that whatever I put in my body is either feeding the disease or fighting it.