Sir synthetic oils are best for any engine, if your pocket allows.
ITs not recommended to change from a conventional oil to a synthetic on in a high mileage engine.
Just follow the mileage mentioned in your owner's manual to change oil (3,000KM maybe), also used a good quality oil filter.
ZIC A/A+, Caltex Havoline/Formula, ZIC HIFLO, SHELL HX3, TOTAL 3000, Castrol GTX, Mobil 1/Super all are good provided they are original (buy from a reputed store like Makro/Metro or a good fuel pump).
Petromin is also providing some very good lubricants both mineral and synthetics, you can get the details by searching in PW forums.
Just calulate yearly expense your budget allows and decide accordingly.