Ok, you have lots of
advice, some of it good.
Disregard the "replace its". Find the issue.
If you start replacing stuff without knowing what is the issue, it can get frustrating and costly.
Very simple to find the problem; Bypass your key, switch, button .,,,whatever, This is done by connecting the main (big fellow) to the positive on the solenoid. It can be done with a screwdriver but best to do it with a wire. If the starter kicks every time you do this, then the starter is ok, the solenoid is ok.....your problem is voltage loss...for whatever reason.
If it does not kick every time, then your issue IS the solenoid.....easy huh?
One possibility is simple voltage loss,sometimes it's a long run from key to starter, simple as that. easily remedied by installing a 30 amp relay at your starter.
You would however only come to that conclusion after making sure all connections are good, all grounds are good, no corrosion etc etc,
The above is easily done at little to no cost.
Have fun