Toyota Repair: Engine Oil /Transmission Fluid and their Additives, lucas oil products, toyota corolla

Question
I own a 1996 Toyota Corolla w/ 135,000+ miles. I've faithfully followed the recommended regular maintenance tasks over the years by always taking it to a Toyota dealer.  It's currently running great.  However, I would like to keep it that way by doing some more of the regular maintenance tasks myself.
Is there a preferred type of engine oil (i.e., non-synthetic v. synthetic) to use for Toyota engines?  Can you mix non-synthetic and synthetic oils?  Are there any additives (e.g., Lucas Oil Products; etc.) that are appropriate to add to the engine oil, auto trans fluid, etc.?
I'd appreciate any guidance you can share.  Thanks.

Answer
I recommend you use toyota's recommended type of oil which is either 5w-30 or 10w-40 regular oil, and change it at the recommended intervals.  I don't see any advantage to switching to synthetic oil other than the fact that you can go longer between oil changes but it also costs more per quart, I do not believe in using additives as long as a premium brand of oil is used in the engine and the atf is replaced in the transmission at least every 30,000 miles.