Can anyone recommend a book on maintaining good relationhip with adult children?

[MariaWaria]

Just that really.

DCs are in their 20s and moving on with their lives and out into their new homes with partners - all good.

Have a tendency to spout my infinite wisdom because I know best so could do with some reading material to guide me.

Any recommendation?

Have yet to come across anything that resonates but you've very wise to start thinking about the issue. For it can be a real issue trying to get it right with adult kids, particularly when they're going through what I call the final separation phase of left home, career, friends, significant other/partner and self financing.
This is the hardest phase to go through in all the years of child rearing. And its a perfectly natural, indeed necessary phase for them because without it, they don't become fully fledged, independent people who are at ease in the world. And there isn't a handbook to help navigate what will be at times, very choppy waters.
So when they start criticising you and rake up incidents from the past where their version of events somehow doesn't chime with your memory; be kind, don't go off on one, listen and don't offer advice, solutions or interruptions unless they invite you to. They are writing their story, their narrative and it won't be, it can never be, the same narrative as yours.
They're trying so hard to be sensible, responsible individuals as they work through their issues, their hopes, their dreams and their new status as independent people and we have to try equally hard to have faith, confidence and trust in them.
I became their unofficial cheer leader. And it seems to work.
Good luck....!!

Why do you think it is that you have trouble refraining from spouting your infinite wisdom? I take it your kids have voiced frustration over this?

pallas what wise words. You sound great and good advice for OP but I was sad to hear its the hardest phase, I'm still messing up with teenagers, now you tell me it'll get even worse?!

I think teenagers are much worse, well mine were. They are all grown up now, two with children. I think the secret is keep your advice to yourself till you're asked, don't expect them to live their lives the way you want them to as they are not you and will make other choices and then be there when they need you.

I think it helps enormously to try to remember what it felt like to be at that stage of your life (and a lot easier than to remember what it felt like to be 18 months).