Unless you prefer to keep to factory spec you could consider going to 15" wheels. All 240/700/900 wheels up until the late 900 series will fit fine and you will have a vast choice of alloys and steels. 15" tyres are much more available than the 14" size which are limited in style and quality. A set of alloys with excellent name brand tyres can often be had from a pick 'n pull for less than a set of budget 14" tyres. It will be down to luck and patience though. Craiglist another option.

Original tire size for a late 1970's Volvo 242 / 244 was a 175/80R14, a Volvo 245 had a reinforced tire in size 185/80r14. A good alternate size for the 242/244 would be a a 195/70r14 and for the 245 wagon a 205/70r14. (see the chart below).
A Mercedes-Benz 240D of that era, used tires in the size of 175/80r14.
A Mercedes-Benz 300D of that era, used tires in the size of 195/70r14.

If they can be found, a 185/75r14 and a 195/75r14 is a good alternative,
A 175/70R14 is def. too short.

Specification Sidewall Radius Diameter
175/80-14 5.5" 12.5" 25.0"
175/70-14 4.8" 11.8" 23.6"
185/70-14 5.1" 12.1" 24.2"
195/70-14 5.4" 12.4" 24.7"
185/75-14 5.5" 12.5" 24.9"
195/75-14 5.8" 12.8" 25.5"
185/80-14 5.8" 12.8" 25.7"
185/80-14 5.8" 12.8" 25.7"
205/70-14 5.6" 12.6" 25.3"

I've driven an '81 242 DL since '85. Many seem to consider the 185/70-14 same as stock and have a diameter of about 23". I always bought all-seasons but also consider buying an H rated tire. They have better all round characteristics than an S rated including stopping in the wet.

Do check the choices and prices on TireRack.com and for an installer near you. They have a good program that guarantees the prices for mounting, balancing, valves, and recycling fee.

according to tirerack the oem size is 195/70-14. What does the manual and door sticker say?