Thanks for your reply. I think what you are suggesting is a straight pole, not one that follows the shape of the bay? This is what we have done in the room above, however we don’t want to do that downstairs as it would mean we can’t use the space in the bay (where the armchair currently sits).
I’m frustrated with myself for ordering curtains with the wrong heading and was hoping there would be some way around it but I guess I might just have to write it off as an expensive mistake .
You did say "pole" so I worked out a solution for one.
You can screw brackets to the PVC window frames. I did. We have a bay window in my "den," (alright...our front room) and our curtains are on a Swish track that follows the bay. Ours was complicated as above the actual window frames it's plasterboard then there's real plaster coving up to the plaster of the ceiling (1960s built house, the original window frames were wooden so the brackets were fixed to them). So the only fixing could be on the PVC window frame and the walls each side of the bay.
But you have to be careful you don't screw into the glass! Don't attempt to screw brackets to the trim between the window frame and the ceiling, it will only be stuck on with silicone.
Swish used to make plastic brackets, but when I wanted to use a longer track a few years ago, they were no longer available. I used their "L" shaped brackets. One screw is enough to secure them as the track stops them twisting.
The short side screwed to the PVC and the track connected to the longer side. You've a few inches to play with, depending on how close you want the curtains to the glass the connecting bit slides onto the bracket and is secured with a grub screw.
I used these photos elsewhere as a solution to someone else's problem.
I bent the track to turn round the corners of the bay.
This required it to be bent first outwards and then inwards to navigate the cornesr. You can see how much the track has to bend.
This was achieved by "wafting it" with a hot air gun, as long as you don't let it melt the plastic!
You also have to keep running a curtain "slider" backwards and forwards along the groove as you bend it, to make sure the bend is not to great to allow the slider to turn the corners.
Although there isn't much room, the rail meets the side walls, so we can draw the curtains back much further than shown..
Right side
Left side