I don't want to drill into the tile either. The tile can crack and it is not guaranteed that won't be a problem. My fairly expensive tile is apparently 'delicate', at that, according to the tiling company. Besides, I might want to do glass doors at some point and wouldn't want to end up with extraneous holes showing. I believe I have seen that where there are old holes showing.

I have a tension rod which has been working fine. It adjusts quite tightly by twisting the multi-piece rod. No labor expense or need to schedule time off from work either. It's a completely flexible installation which is always a plus with me.

The curtain is not heavy though.

You can get ceiling mounted curtain rods. They are sometimes expensive, but Umbra makes one as well. But I've never understood why people don't want to mount a shower curtain rod. If you take showers you have to use a curtain and they are a standard size, it's not like it's something you are ever going to have to move and be stuck with holes.

I have a curved shower rod (LOVE!!!) that is drilled through shower surround tiles into the wall.

When my bathroom was remodeled, I did not, in the worst way, not want to drill through new tile. After trying to make tension rods work, I gave the go ahead to drill, baby, drill. I couldn't watch. :p

No tiles cracked. The holes were put in the right place the first time. I have a nice light shower curtain, use the shower everyday, and have no worries. It's secure.

If it is just sliding because you can't safely tighten it more, I suggest you get some silicone caulk in a tube and apply some to the part that contacts the wall on both ends. Then put it up and tighten as before and smear off the excess caulk That will safely increase the grip to the wall.