Broken bed

Any decent wood merchant could cut you that over the phone, call and collect. They are open, classed as DIY providers. Then it’s just a case of rubbing down, applying a finish and putting back into place. Shouldn’t cost much.👍

Go to the local DIY store ( thats open ) and get them to cut a piece the size you want. they may even have an offcut thats close to size that they can trim to size for you. 

Have you looked at chipboard shelves/boards in B&Q they do different lengths and widths,  ours are open in his area

£25 will buy a jig saw and reduce faff. 

Use the old , or take it to DiY shop as a template.

If half inch and likely to be sat on I would want plywood rather than chipboard over that span

Use plywood as chipboard at 1/2inch is not load bearing and you will get a better finish to the edges and any decoration you do to the board.This is a simple job you can do with basic tools 

B&Q will normally cut pieces to the length you want if you buy some timber the correct size,  but maybe not right now.

Marine ply might be the better option stronger  but slightly more wexpensive. 

OK, useless info. About 30 years ago I was staying with family on a CL in the North of England. The table made up the base of a double bed and rested on two strips of hardwood screwed and glued onto the face of the front bench seats. The glue on one side had dried out and whilst halfway through a morning cuppa whist sat up with my brew the strip towards the head end gave way. I went down, the cup went down and the tea seemed to remain in the air and then drop back into the cup. We drove later to the nearest small town. No wood available but bought some brass screws and adhesive. Rooted through the town and found a builder chap renovating a property and asked where I could buy wood. 'Nothing local but grab a pint and come back in half an hour'. 

Took family to local pub, ordered the food et and a pint for me. Went back to the builder and he said to jump in the van. He drove about 7 or 8 miles to where the local coffin maker was. He rooted through his stock and brought out a matching strip of hardwood. No charge. Builder drove me back stopping at his home and made us both cheese and onion sandwiches before driving back to his job. What do I owe I asked. No charge. Gave him 4 tins of beer a a thankyou. We went back to site and borrowed a hand brace and some bits and a saw and repaired the van. Don't you like nice folk.