Ok, so the first thing you're going to want to look at is proper storage that is both discreet and dry. Somewhere a visitor, particularly a child, won't randomly get their hands into without at least first taking part in some serious ransacking. The dryness is important to the longevity of any silicone toys, and that can be supplemented by lining the storage area with a towel. Only ever store platinum-treated silicone with it's own kind, but we'll get into silicone details later.

Next is lubricant choice. For lube, anything water-based is fine but you will probably want a thicker lube (typically marketed toward women if the marketing is gendered) because it tends to stay on penetrating toys a bit better. Gooey lubes are also good so long as they are still water-based. Bad Dragon's cum lube is a favorite of mine, but I tend to just go to my local brick and mortar to pick up whatever. In a pinch you can use a cooking oil, but this will permanently stain fabrics.

Always go for platinum-treated silicone, also known as "medical grade silicone." It is more expensive than normal silicone or other materials but it is worth your money. The toy will last longer and be more bodysafe than anything else you could use. It will also be possible to clean it thoroughly enough that it can be used orally or vaginally after it has been taken anally so long as it is cleaned first. You will also need to purchase toy cleaner to do this properly.

So what size of dildo? Well, for anal, thickness is FAR more important than length. If the dildo can bend then it can be pretty goddamn long, that is part of the entire concept of anal beads. Thickness should be your primary consideration. A normal human penis-shaped dildo would be fine for that, but if you're like me and prefer more... exotic cocks then the ideal shape would have a tapered tip, a smallish shaft, and some kind of expansion near the base. Have a cat safety-inspect your dildo.