Be careful about mixing different types of coolants, especially with the older green ethylene glycol based ones which are still quite appropriate for our old Volvos. Mixing some coolants can actually result in jelling. You need to match the coolant type to the variety of materials used in the cooling system (steel, copper, aluminum, plastic, soldered joints) to provide optimum corrosion protection and more importantly to avoid leaching and prevent oxylates from forming. That's why some people prefer to stick with Genuine Volvo coolant designed for the way our car cooling systems were originally constructed. The newer orange DexCool-type coolants designed for primarily aluminum systems are generally not appropriate for our old Volvos.

Extended life antifreeze, claiming adequate corrosion protection for 5 or even 10 years, is what I tend to use, but there's absolutely nothing wrong with using everyday 2-3 year antifreeze if you're willing to change it frequently.

You should always do a thorough flush before changing coolant type, in fact always best to do a thorough flush every time you change the coolant, but I can also sympathise with the OP not getting too excited about perfectly maintaining an older car not worth overly caring about.

One other tip I'll add here. It's best to use concentrate rather than using 50/50 pre-mix, especially in extremely cold or extremely hot climates where it's best to try optimizing freeze protection and boil over protection. Because the cooling system is rarely fully drained, and this is especially true after a flush, there may be a lot of residual water or old dead coolant still in the system (especially the block and heater core). Sometimes as little as only 5-6 litres needs to be added to top up a 9.5 litre capacity system. If you were to use 50/50 pre-mix for the whole system, you might end up with as little as a 30% concentration. To best achieve the recommended 50/50 mix, you start by adding one half the cooling system capacity (4.75 litres =5 qts US) of concentrate then top up with water. Distilled, de-mineralized or soft potable tap water (such as adequately filtered and treated water from rain fed lakes and streams) is preferred, and in that order of peference. Always avoid using hard tap water (such as from ground water fed systems and wells) to prevent mineralization. Absolutely avoid using de-ionized water to prevent leaching. And that's not to even mention that buying concentrate is generally a lot less cheaper than buying pre-mix for the job, even when it's on sale.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now