将字符串存储为c#中的UTF8

I'm doing a lot of string manipulation in C#, and really need the strings to be stored one byte per character. This is because I need gigabytes of text simultaneously in memory and it's causing low memory issues. I know for certain that this text will never contain non-ASCII characters, so for my purposes, the fact that System.String and System.Char store everything as two bytes per character is both unnecessary and a real problem.I'm doing a lot of string manipulation in C#, a