Degenerative Myelopathy

I have a 10 year old Great Pyrenees. Her mobility is declining. But she looks SO happy. She wags her tail, eats, plays, chews on her favorite bones, loves belly rubs and star gazing. All the things she always loves to do. She can see and hear but her back legs are going… we have all hardwood floors so she slips and 50% of the time can’t get up unassisted. When she goes outside to use the bathroom 25% of the time she will fall into her pee or poop. I just feel like she has more life in her, do I buy her a wheelchair? I understand quality of life and I just feel like her quality of life is great outside of the whole walking thing(she’s not an active dog as is, she’s very happy people watching if you will) but I obviously want what’s best for her. How do you Iknow it’s time? I don’t want to play god and in my opinion, it’s not fair to her to end her life, if she’s not ready to go. If she wants to live, I want to make her comfy. what was your experience?