How to set alarm sound to lowiest as possible

there is 2 types of alarms. Sleep&wake up and Other. I use first one every day and works fine. But every thursday I have to wake up earlier. I can't set volume of alarm, it is connected with call sound volume. Each time I need important call I increase volume and each time on thursday alarm wake me up in maximum volume alarm! my pregnant wife gona kill one day or I have to buy Android. If somebody have solution please share. Tried apps, but no luck, they all use core iPhone alarm functionality. I found somewhere if you select alarm tone and lowering volume it will help, but didn't help. Because if increase ringing volume you will increase the alarm sound as well. It shouldn’t be that way. Lost simple functionality...