You need not cut your hair before mikveh immersion, even if it is long enough that you feel it needs cutting. Since you strongly prefer to have your husband style your hair, you should wait until after mikveh when it is
permissible for him to do so.
However, you should not schedule a haircut within a day of immersion. According to some halachic opinions, hair that a woman has immediate plans to remove (within a day) is considered something she is particular about (
makpidah). When a woman is
makpidah about something, it can be considered a barrier to immersion (a
chatzitzah).
Please write back with any further questions.