Winnie, great news - though I well understand the sense of apprehension about returning to work again. Been there, done that!
As Batters says, writing everything down, going for a few hours the first days and taking a favourite toy are good ideas.
Also consider taking favourite drinking cups and blankets.
Get your childminder to write down you son's day-to-day routine - sleeping, feeding, dirty nappies etc. It's very reassuring and helps you seamlessly enter a good bed time routine - eg: prevents you feeding him a big supper at 7.00 pm without realising that he had a meal at 5.00 pm - and clearing up the resulting mess when he sicks it up in his cot! ( I speak from bitter experience)
It's a good idea for your son to see you are very happy with this new person in his life, before you leave him alone with her, so be extra friendly when you first introduce your son to her. You could also think about leaving something familiar, like a scarf, to reinforce the fact that you are coming back.
Now I hope the following point is not too much of a downer, but it concerns something that's happened to me twice, so I thought I'd pass it on.
Assuming you like and and trust your childminder, be really supportive and ultra aware of any concerns they raise. By the time each of my sons hit two, their respective childminders gave in their notice. I was probably just unlucky. But in each case, much of the reason boiled down to the fact that they found my son too much of a handful. It wasn't that they felt my son had problems, or that I could have done more my end, but their transformation from relatively easy baby to more-lively-than-average toddler was simply too much for them. In each case I offered more money or a reduction in hours. No joy!
Both sons appear to have suffered no ill-effects from having to change childminders, but obviously continuity of care is desirable.
It's worth bearing in mind that both these childminders were good, but fairly inexperienced. One was a friend and neighbour, the other was registered. If I was choosing a childminder again, I'd definitely look more favourably on one who's been doing it for years.