Can I replace a 90×190 mattress with a 90×200 without buying a new bed?

In some cases yes, depending on the construction of your bed frame. Some frames have a flexible slatted base that can accommodate a slightly longer mattress. In other cases, the frame has a fixed headboard and footboard that limit the length to exactly 190 cm. Measure the interior length of your bed frame carefully before ordering. If the frame is fixed at 190 cm, a 90×190 mattress remains the correct choice.