Ah, Volvo 240 seats!
We all wish we'd bought from a car driven by a 95-pound woman, only on Sundays.
Instead we get one driven by a very large person who must have squirmed around a lot.

Anyway, the most likely solution is to buy a passenger seat of matching material. Or driver + passenger seats, both CLOTH as you likely have vinyl. You'll like the cloth if you ever get to try it. Especially in hot or cold weather, it's more comfortable. Usually seen on sedans, most wagons got vinyl.

You can swap covers left to right, you'll only need to make a hole for the lumbar adjuster. If you like you can put a patch cover under the old hole that's now on the wrong side - it will be on the "inside" where it will rarely be seen.

You can wash the cloth upholstery in a washing machine after removal from the seat. Probably should air-dry as it seems to be all synthetic.

I don't want to swamp you with seat restoration details - but we have the details, when you're ready to spend a day or a weekend on it. Usually by now the foam is pretty well ruined and needs to be glued back together and reinforced with cloth backing - that's the short version.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.