Remathilis
Legend
The problem is that daily spell slots are multiplier, not additional. At level 7, 3 slots per day becomes, 6, 9, 12 or more depending on how freely you can take SR.It is a possible solution, but I don't know whether it would be too similar to daily spell slots to be accepted.
I definitely don't see a problem with increasing the Warlock's overall number of spell slots by like 1 or two.