I have a small black insect in my bedroom mainly ...

Probably not since this is only one; mites come in groups. But more important, mites are tiny. Why don't you kill this insect?

It might be bedbugs.  Google "bedbugs" and you can find pictures of them to compare.

insects have 6 legs, mites have 8, and, yes mites are related to spiders but don't look much like them.

Garden mites are orange or red.  Most other mites are white and you generally cannot see a mite until you are right on top of it.  Many mites are actually too small to be seen by eye alone - eg bed mites.  Your little friend sounds like an insect that got lost.