Mic only with double bass is really problematic. You've better off just using a pickup or up blending a mic with the pickup to add some 'woodiness to it.
With an amp As well you are just asking for feedback.
If you insist on this route then you'll need to buy a decent EQ / pre-amp with a least one notch filter so you can start to isolate problematic frequencies. You might consider an F-deck as well (search this forum) and a bass specific mic.
Good luck....