Hello everyone!!

I adopted an elderly cocker about 3 months ago and this is my first ever long-haired dog.
I started off grooming her daily with a regular brush (it has two sides - one with soft black bristles and the other with hard metal bristles). She was never keen on me grooming her legs (understandably). However, after not too long, she was diagnosed with breast cancer and needed 2 major operations, so I stopped grooming as much to avoid any extra stress during her recovery. Fast forward to now - she has a LOT of matts and clumps that I will have to clip out and I am not managing this wild fur!!
I bought a conditioning spray that can be used wet or dry but unfortunately it doesn't seem to do much at all.
I've read through some of the pinned posts here but they seem a bit more geared to grooming for a professional kind of look. I don't mind how she looks, I just want her to be comfortable.
Does anyone have any advice for easy, inexpensive and most of all, pain-free / stress-free grooming tips? I wonder if I'm even using the correct type of hairbrush, for example. I just want to be able to maintain a healthy coat once the matts are clipped out and avoid it happening again.
Thanks!!