A 3/4" drop across the width of a toilet indicates a huge structural problem. I won't ask why you choose not to deal with it, but I can tell you that everything you have suggested would be look like hack job with doubtful success. You can put all the lipstick in the world on a pig, but when you're finished, it's still a pig. I realize this a very negative response to your question, but unless you deal with the cause of the problem, nothing is going to make this at all workable. Plumbers deal with slight variations in floors all of time with shims, but we're talking like 1/8" up to maybe 1/4". Leveling the floor is not a DIY job for a person with little or no carpentry skill and basic tools either.