Yeah, a simple checkboxes field with a list of the countries would be a good approach to realize this.
Another idea is to make use of the localization feature, which comes with a Craft Pro license. Then you'd add a new structure entry (in your case the product) in one locale (e.g. "fr"), save it, and all entered content is copied over to the other locales (e.g. "en" and "de").
After that you can switch over to another locale's version of that entry, and make individual edits for it (e.g. change "10 EUR" to "8 GBP"). To disable an entry completely for one locale, use the status lightswitch available for each locale separately at the top right of the info panel.
Don't read this as if this "localization feature" solution is the right one. Consider if you really need to translate entry fields (product infos etc.) into other languages1, if not I'd definitely do it like you initially intended.
And there's also a chance that you want to use both of these features combined: if you want to list all entry pages translated for each locale and additionally show the visitors where these products are available.
1. "Craft Personal and Craft Client store content on a per-locale basis too, so down the road if you want your site to cater to a second locale, Craft is already set up for it."