That’s correct, sleeve surgery removes around 75-80% of your tummy but gastric bypass creates a much smaller tummy from your tummy & attaches it to your rerouted intestines. Your remaining tummy is still there after bypass but no food can enter it. Further conversations with your surgeon may be needed to help you understand the differences in the surgeries, how they impact your body & which may be best for your needs. It may help ease some of your nerves too. (Nerves before surgery are very common - fear of the unknown, uncertainty, etc.)
With both surgeries your ability to consume large portions is reduced. Initially after either surgery when you start consuming purées you will only be able to eat 1/4 - 1/3 cup of food. This slowly increases. (By 6 months I could eat about a cup of food & now I eat about the recommended serving size or a little less.) And it is possible for you to eventually eat around your smaller tummy which of course results in weight gain & something to be aware of.
Changing your eating habits, your relationship with food, understanding the nutritional benefits of food, etc. are vital aspects of losing your weight & maintaining the loss. This is the work you have to do & has nothing to do with the surgery. Many find the temporary changes to our sense taste & sometimes smell after surgery is an opportunity to try different & healthier foods. I have some food sensitivities so I recognise you may as well but are they legitimate food sensitivities or just you don’t like to eat certain foods (taste, texture, etc.)? A dietician can help with this as well. Often working with a therapist is very helpful to work through your relationship ship with find & what is behind your eating habits., as well as your hunger (distinguishing between head hunger & real hunger).
Focus on eating your protein first at every meal. Then eat your vegetables. Finally if you are able eat any carbs. This will be the same advice you will be given after surgery & when your able to eat solid foods. There were many meals I only ate my protein & couldn’t or didn’t want to eat anything else. ( I still have days like this almost 4 years out.) Start tracking your food (portion sizes, calories, protein & other macros). There are some great apps you can use.
You can be successful with either surgery but after the honeymoon stage when things like your appetite returns, most of your success depends upon you. You have to be ready for the surgery & the changes it brings & the changes you have to make. Surgery was the best thing I ever did.
All the best whatever you decide to do.