You asked a huge question that only you can answer and that was will you get use to going slow. Only you can figure that out. I'd suggest some chartering of other boats, different styles and likely slower. We chartered one slow boat and figured out very quickly we could not get use to slow and we were coming from a background similar to yours of faster, under 30' boats.
You're going to find the majority here are going to warn you about fuel costs, a legitimate warning, but also tell you how wonderful slow is. That may be true for them, but doesn't mean it will be for you. You'll have to answer that question. You are also the only one who can determine if fuel cost will be a deterrent to boat use.
Now, all 42's are not created equal. I don't know what brand you had for the sea trial. However, sometimes the faster boats have less usable space. Doesn't have to be that way, but it's a common design characteristic. Regardless, you'll have to go by your own feelings. If you try a 45' trawler type boat and it's too small and too slow for you, then don't argue with your feelings. Move up in size and speed.
You indicate the following three things. 1-42' flybridge too small. 2-question getting use to 8-9 knots. 3-have settled on trawler design. Well, news flash, those three don't go together. You have to decide which are the important items. We would be in the great minority here to feel as you do on 1 and 2. That's why we don't have a trawler design. Instead we have what might have the space and sea worthiness needed but in a larger and faster boat. As others have pointed out though, it all comes with a price. And it's not just a purchase price, it's an ongoing operational cost.
That's where you must temper your desires with realism and with your own budget. Just don't underestimate the annual operating costs. Don't get a boat that makes you worry about costs or even use it less because of the expense of usage.
So, look realistically at your desires and back up a bit to list all those things important to you in a boat. List those that are absolute necessities vs those that are desired but you could live without. Don't start with size as a requirement. Start with what you need a boat to do for you. Then you'll determine what styles and sizes fit your requirements. How many does it need to accommodate comfortably and for how long at a time, how large must the stateroom, galley, salon be, must it have a flybridge, where do you like the galley, how long at a time should you be able to enjoy being out on it, how long must it carry food and other provisions for.
The more boats you can get on, the more you'll figure it out. You may do it more at first, not through what you like so much as through what you don't like. So far, you've been on one 42' boat that you wouldn't be happy with because....because of what really, though? You said too small. That means nothing that helps you. In what way was it too small? What would it not do that you required? Not enough storage? Salon too small to be comfortable? Galley too small for your cooking desires? Bed in stateroom too small? Or did it just feel claustrophobic to you?
Good luck in your search. Remember one thing very important though. Only you can ultimately figure it out. Do not let others dissuade you from your own preferences. Find the perfect boat for yourselves, not for anyone else. We did the loop in a boat I don't know of anyone else ever choosing to do the loop in and can't imagine they would, but it was perfect for us. However, we're also the only ones I know who did the loop and never had fewer than 6 people aboard, and as many as 8.
There's no such thing as the perfect boat. Not perfect for everyone. Find the boat that comes nearest for you. You and no one else. You'll be able to do it.