The most popular & affordable choice is a counter top microwave. Since it can take up a lot of counter space decide how much you can spare before buying.
Over-the-range microwaves fit over your stove & have a hood built into the base - a counter space saving design. They cost more & may need an electrician to install.
If remodeling, a built-in microwave can be installed in custom cabinets. They have unfinished sides, but due to being less popular, they are costlier.
For reheating foods, a smaller oven works; meals need a full-size model. The interior is measured in cubic feet & more watts means faster cooking.