@Glenda35
I am afraid you simply have to wash any bed linens that the guest may come into physical contact with in between every stay. There's just no way around that.
Personally, I would not have a quilt without a cover and rely on a top sheet. There's been a lot of discussion about this already on the CC. People have different preferences for how they sleep and some guests will pull away the top sheet and sleep directly under the quilt. Even if they don't do that, guests might eat in bed, put suitcases or other items on top of the quilt, sit naked on it or even have sex on top of it!
If you're going to use a quilt without a cover, you should wash it every time. It's so much easier to simply have a cover and wash that. It might seem a bit of an effort, but that's just part of hosting and I'd think a pretty standard part of a turnover.
As for winter/summer, I have lighter duvets for summer and heavier ones for winter. The lighter ones then go in the cupboard so the guest can use them as an extra layer if they feel the cold easily. Of course, you need the storage space for this to be feasible.
There are lightweight bedspreads as an extra layer at any time of year, but I host long term stays, so it's not difficult for me to wash these in between stays and I would maybe skip them if you have a lot of turnover.