I can see why you'd like to get both surgeries over with at the same time. I'm not a baby about dealing with pain, etc. (ex. I had my last endoscopy without sedation), but I would definitely not recommend the tonsillectomy at the same time as the Nissen. The Nissen is very manageable, but the tonsillectomy is very painful. Doing them both at the same time is asking a lot of yourself. There are some surgeries you could combine, but two that relate to your throat and GI tract is not a good idea. Yes, the diet would be similar, but it would make your recovery from both that much harder. Each one separately would be challenging, but together you're probably asking for trouble. I'd take the advise of your surgeon.
Sorry I can't tell you what you'd like to hear, but you asked for opinions, and that's mine.
Good luck with your decision!
Take care, and best wishes with your surgeries.