This is one of my fears because my bedroom is also upstairs and the dogs go with me. I would say it's probably a combination of both things. If it was just sight you could just guide him up slowly and the same if it was just his legs. Since he seems to want to go with you I wouldn't stress him out and I would just help him along. You can use just a towel and guide him up. For arthritis my vet recommended fish oil, she said that everything else is hit or miss but fish oil works. Sending positive thought to all of you and a hug for Lucky.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD