Most trash service was set up when the house had two adults, or more, and it stayed that way after the bin came with the house. A bin sized for a family can be far more than one person fills in a week. That is not a problem until it is a problem: a bin that sits half empty is a bin that gets heavy in the wrong places, and a full bin is a hard thing to pull to the curb if you are the one who has to do it.
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Count what actually goes out
For a week or two, keep a pail by the back door and count what goes into the bin. Be honest about the food scraps, the packaging from takeout, and the cardboard. Note which days the bin is full and which days it is nearly empty. That count tells you more than any guess about the size you need.
Compare the bin sizes and the lids
Ask the trash company which bin sizes they offer and whether the size can be changed later. Ask what happens if the bin is overfilled or if the lid will not close, and whether they will still pick it up. Find out whether a smaller bin picked up more often is an option, since a smaller load can be easier to handle than one large bin that sits too heavy to move.
Think about the wheel and the walk
Look at the path from the bin to the curb. A bin with wheels that rolls over the lawn is easier than one that has to be lifted over the step. Check whether the bin has a handle that lets one person tip it without straining, and whether the lid stays up when you empty it. If the walk is steep or the driveway is uneven, mention it to the hauler and ask whether they will take it at a different spot.
Recycling and yard waste
Decide whether the recycling bin is still needed at the same size. A household of one often fills a recycling bin more slowly than the trash, and a smaller bin may be enough. Ask whether yard waste is picked up on a separate day, and who will move that bin when the weather is bad.
Set the pickup routine
Put the bin day on the calendar where Dad will see it, and decide together who takes the bin to the curb and who brings it back. Many of these jobs go wrong because nobody owns the bin on pickup morning. Make it a small, shared routine rather than a chore that falls on whoever notices it first. If he insists he can handle it, let him, but check the weight of the bag before he lifts, and offer to carry the heavy one yourself.