若要表示“……得多”“更……”，比较级前可用much, even, still, far, a lot, a good deal, a great deal, rather等修饰。如：

It’s rather later than I thought. 这比我想的还要晚。

You’re looking much better since your operation. 手术后你看上去好多了。

He is fat, but his brother is still fatter. 他很胖，但他哥哥更胖。

It was cold yesterday, but it’s even colder today. 昨天很冷，今天甚至更冷。

Everything was a great deal simpler many years ago. 许多年前，样样事情都要简单得多。

There are far [a lot] fewer accidents in modern factories. 在现代的工厂里事故少多了。

http://www.yygrammar.com/Article/201103/2045.html

【答】你的老师说得没错，不能说 more better，因为 more 不能用于形容词（或副词）比较级的前面，better是good 和 well的比较级。《朗文当代高级英语辞典》第5版指出：“more 不用于 形容词或副词的 -er 形式之前： Driving is cheaper (NOT 不说 more cheaper) than going by rail.开车比坐火车便宜。”

better 就可以表示“更加好”的意思。