maybe a factory reset might do the trick.

as for an upgrade, what is your price range? do you have a particular brand? carrier?

 

Are you by any chance using a third party launcher, or other apps such as calling apps, messaging apps, or any other that runs continuously?

I ask because on a low performance device there are some apps that use way too much power for such devices.

Case in point, I had a phone with 1GB of RAM, and I really liked Apex Launcher.

The phone had most if not all of the symptoms you describe, even if I got rid of almost all my user apps.

I later discovered that while Apex Laucher itsrlf only uses about 30MB of RAM, the Google Analytics built into it used a whopping 200MB of RAM all the time!

Together, that makes about 25% of the memory used.
Now add whatever the system needed to work.

No wonder that poor phone was acting up!

So, I ditched that launcher, and now look for apps that do not have Google Analytics built into them.

It makes the device much happier, I am much happier, and Google can get bent for all I care.