I am goingt quoat neil peart on this and say
you will never stay perfectly with a metronome or your going to make yourself crazy trying to.
Keep the same tempo thru a whole song is just somthing that takes time to learn.
I have gotten to the point where I keep a great tympo and have had many bands love me for that but I almost never worked with a metronome.
I use mine to maby get the right tempo to a song.
Guitarst on the other had have a hard time staying in tempo when they p[lay by themselves so I tell them all to practice with one
I would say just keep playing with the music on your records and you will get a good internal tempo going.
But by all means get one to take with you they can be very helpful at times.
and I would ay that the cheapest easist one that I fond is a little blue one by korg. I think I only payed like 20 for mine and you can plug a headphone in to it.