Your questions apply not only to the sleeve procedure.
The good news is that you don't have to put yourself through the anguish and doubts you've taken on. You can decide right now not to have surgery. It's that simple and freeing. In fact you can choose not to lose weight by any method. Even simpler and more freeing. No matter how one chooses to lose weight, a lifetime commitment is necessary for lifelong success.
The greatest obstacles are emotional, not habits. If chewing mindfully and thoroughly is "unnatural," then the converse must be true. To eat "naturally" is to bolt food mindlessly à la the wolves. People have the capacity to develop new habits by repetition. Eating in the ways that suit surgery can become the norm when you desire. It's like learning arithmetic. We eventually rely less on our fingers for counting.
"Large amounts of time and energy" for planning meals? You really won't have to pass up other activities to have time for all that ponderous planning. As feeble an excuse "I have to wash my hair" was in the olden days, "I have to plan my meals" has less credibility.
I'd be dishonest if I were to say that making changes is a snap, but it's nowhere near what you're telling yourself. It's okay to be ambivalent and fearful of making the commitment to yourself, but don't do yourself the disservice of being dishonest with yourself.
It might help you to make a decision if, instead of listing the negatives, you begin a written list of reasons that you do want to lose weight. Keep each reason brief and narrow and number them as you go along. Pick up the notebook over the next days and weeks to add reasons as they occur to you. No reason is silly or shallow. They're all about what you want for yourself. Wanting to wear size 6 knickers is as valid as wanting to be rid of backache or signs of diabetes.
As an example of focused reasons, "To wear the blue dress that's been hanging in the closet these past four years." To write "To wear the things that got too small" limits the number of items on the list. Name each separately if that's the case.
If you're feeling that you're jumping in to something that you're not ready for, give yourself more time. You want walking into the operating room to be a positive experience, not a trip to the guillotine. You're ahead of the game in knowing that behavior changes are necessary, but don't blow them into impossible tasks. You may very well run into rough spots and feel resentful from time to time after the fact. That's what the therapist, BP and your surgery practice's support group are for. We each have to do our own work, but there are others to do it with.