Have a look on Lazada, both OPPO and Vivo are good phones, I've bought a few for my gf and her family.
Make sure you read the comments and pay attention to the stars.
Watch out for copies and non genuine models, fakes with slight spelling differences eg. OPPQ
Then put the model into this website, it will give you the Specs, ram, Rom, CPU, usb c or micro connection etc.
https://m.gsmarena.com/