Child's bedding for a single bed

[Thistledew]

We are moving DS, age 3 to a proper single bed from his toddler bed.

What sort of mattress, duvet and pillow is suitable?

Is it worth spending on a good quality mattress now or is it best to wait until he has stopped the (occasional) wee accident and stopped using his bed as a trampoline?

The duvet he has on his bed now is a toddler one and I think just 4 tog - but most standard ones for a single bed start at around 5. Is this ok now he is a bit older?

What about pillows? I don't think he needs or would like one that is any deeper than the toddler one he has, but I've never seen very thin ones in a standard pillow size, which makes buying standard duvet and pillow case sets a pain.

You can buy mattresses that have a zip off waterproof topper which are invaluable throughout childhood - even when they are reliably dry at night, there will be tummy bugs etc.
All the families I work for have usually just used a normal duvet and pillow when they've moved children into beds, probably a 9 tog? Cheap pillows tend to go very flat, very quickly and a lot of kids prefer flatter pillows.

We just bought everything like we would for an adult, though our dd was closer to 4 when she went into a single bed. Mattress was just a standard one from IKEA. We got a waterproof mattress protector (I forget what brand but they are ones that are basically just a fitted sheet, not plasticky, soft like normal fabric, just search on Amazon). Then normal pillow and duvet, though I think she kept her cot bed duvet for a bit as the single sized one was massive to start. Bedding all just came from IKEA or Next, wherever I could order it online. Mine is 6 now and regularly uses the bed as a trampoline, so I don't think there is any reason to wait, but we didn't get a super expensive mattress either (was maybe about 200).

Ikea Hovag mattress (so good, I have the king on my bed!) and then a waterproof mattress topper with standard kids bedding.

Single duvets start at 4.5 tog do it depends on what he likes

DS is a sweaty Betty so has never used his 9 tog. You can also get waterproof covers for duvets. A godsend if they have accidents