Our 20-year-old kitchen back door is made of hardwood, and has a hardwood frame too. The door is holding up well, although it needs some TLC after the last decorator did a cheap and nasty over-painting job on it. The frame and step, however, are in a really bad way; replacement is the only option. The house itself is of a modern appearance, and all of the house windows are uPVC, so we really have two options:
The first option would clearly be a cheaper option, but would probably be more fiddly to make the existing door sit nicely in a new frame. The second option, despite being more expensive, should be a straightforward off-the-shelf job, and a glazed door would get more light into the kitchen.
A uPVC door would need to be "toe and heeled" - see the Glass & Lock Co's How to toe and heel a door or Window for a guide. The size of hole that we need to fill is 920 x 2095mm. Example door and frame kits for around £250:
Alternatively, we could buy a new hardwood door frame set, to fit our 33" x 78" door.