I find that my domes tend to slip a little if they’re not cleaned every day. I remove them every night and wipe them down with the same wipes I use on my CPAP mask, which seem very effective at removing wax and oils, and replace them before putting them in the storage case for the night. That way I have them fresh and ready-to-go the next morning.
The other thing to consider is that, at least on my Oticon aids, the receiver wires can be shaped to the contour of your ears. I have simply bent the wires slightly in so that they keep the domes more firmly in the ear, and also shaped the wires to fit more snugly against my ear. I understand that one can heat the wires on an Oticon aid (being careful not to damage them by overheating) to make them easier to shape, but I have not found it necessary for the minor adjustments I’ve needed; if I did, I might ask my audiologist for help.