Lawn problems

Last  year I kill off my lawn I did not know but it was at the start of the drought I have bought grass seed from a well known fIrm asking for a slow low growing grass. When the same trough there was a lot of fast growing broadest grass is left any way to kill if the fast growing grass with our damaging the low growing grass. Thanks in advance I'm 85 health not too good unable to keep up to maintenance of long grass can any one give me any ideas what I called do.  I have 17 means of seeds but don't want to set it because of the first lot I put down. The broad leafe grass is taking over lawn