Right click on the channel icon and go to 'Notification Settings' rather than clicking on 'Server Mute'. From there you can choose whether a mention (inc./ex. @everyone/@here) counts and whether mobile notifications are enabled.
As for the client you may want to try Ripcord[0]. It uses less memory though I'm not sure you can mute people the same way. While I don't think it's ever enforced, technically using other clients is against the Discord ToS.
Either way there are plenty of reasons not to use Discord if you can.