Not sure your nationality and what will be too heavy. But Jamaican black castor oil is wonderful with growing and maintaining thickness, but it is very heavy. You must maintain a routine of at least once a day or a few times a week. You can use the Jamaican black castor oil in the bald spots and maybe something lighter and your whole head.
I'd say to give rosemary oil a go. It's light weight and helps with hair growth and thickness.
Oiling your hair but it is a waiting game I’m 9months pp and it’s all finally growing back