If you are going to get the custom moulds free or not too expensive then I’d say give it a go, the worst that can happen is you go back to how you were. If they are going to cost you a fortune then that’s rather different.
I have always found custom moulds difficult because the shape of your ear changes when you do things like chew food and change facial expressions. I found I couldn’t smile with the aids in or they’d pop out, so I started trying to hold a cheesy grin when I was getting the moulds done and that worked a bit better but then they were not such a good fit. Then again we get the cheapest rock hard moulds here, so there’s a good chance that softer moulds wouldn’t have that issue.
You also have a larger tube coming over the top of your ear as there is a hard “elbow” attachment on the hearing aid attached onto the larger tubing, which can irritate some people, especially if you also wear glasses as there’s a lot to store behind your ear when you are not used to it. Only time would tell if you’d get accustomed to it or not.
You could ask them to make a small “canal only” or “canal lock” earmould. Hopefully this doesn’t look like I am making an ad for this company, I have no connection with them, being on the other side of the planet, I just find it a really useful picture of the different types of mould that can be made, as there’s some variety within the custom moulds. There is also a variety of materials from hard to soft - harder is generally more durable but what price comfort?
Again, if they are going to supply them under some kind of warranty or insurance that you can get a larger one done if the small one creates problems then I’d start with a small one, but if you have to pay for it then you might be better asking for a large one, as you can always have bits drilled off and filed down from a big one.
You may also find it cheaper in the long run, as replacement tubing for a custom mould is an off-the-shelf commodity that you can retube yourself with a little know-how and a small tool, not sure if the rest of the world has the expression “made by the mile and cut off by the yard”. Thin tube fittings are manufacturer-specific so they work out more expensive over time for replacements.
You would almost certainly get better retention from a custom mould if for example you do sports, as the thicker tubing, hard elbow and custom fit makes it far harder for the aid to flap about. I have had to tape my aid to my head to manage with the thin tubes.