Hi
I used to do similar to Sylvia with my mum .
I would back mum up to the bed, this may sound strange but I did this from her side, you might find it easier supporting your wife from the front, also you can sit her down much easier if you are in front of your wife.
Fortunately my mum would sit down when she felt the bed touch the back of her legs.
Once mum had sat down, Whilst my arm was around her back hand under her armpit furthest away from me, I would lift her legs and swivel her round.
YOU NEED to be careful of YOUR back though.
ALSO it is possible to cause shearing of your wife's skin
When I received amongst other things a Hospital bed and a slide sheet, it made things a lot easier for me.
The hospital bed was brill, I could adjust its height so that it was at the right height to get mum in and out of bed, the right to make the bed, turn mum, massage her and hoover under the bed.
Mums would nearly turn into a chair.
You can get the above and more on loan from the NHS loan store
If your wife has visits from a Community/district nurse , they can suggest and order equipment.
If no community/district nurse visits, then DO speak to the GP as they can arrange for someone to come out and do an assessments for the equipment that you may need to help you.
My apologies if you already know this.
Hope this helps