Unless an abundance of internal storage is a priority for you, 256GB should be enough. This model packs some great hardware with a 3 GHz octa core processor.
From Amazon
POCO F4 GT 5G - Smartphone 12+256GB, 6.67” 120Hz E4 AMOLED Display, Snapdragon 8 Gen 1, 64MP Triple Camera, 4700mAh, 120W HyperCharge, Stealth Black (UK Version + 2 Years Warranty)
OnBuy
POCO F4 GT 5G - Smartphone 12+256GB, 6.67? 120Hz E4 AMOLED Display, Snapdragon 8 Gen 1, 64MP Triple Camera, 4700mAh, 120W HyperCharge, Stealth Black