I'm with you on the no fly thing - I haven't flown for over 20 years and I don't care that I'm missing out on some long distance places that I'd like to have seen - I just don't want to fly. Like you, it's not about the flying, it's about the dying. And as I knew several people that ended up dying in aircraft crashes (different people in different crashes, not just one family in one crash) for me personally, it's the form of transport that has been the most dangerous to the people that I know. And yes, I know that statistically (depending on the stats you use though) it's claimed to be the safest - but I'm an outlier for whom it isn't - and that makes me perfectly happy not to fly.
Anyway - I've still managed to have great holidays - albeit more of them were pre DC, who are still quite young so haven't got as far afield again.
Cruises are amazing. And big cruise ships are a very different prospect to even sailing on a big ferry, it has to be really quite stormy before you feel that you are on a ship to feel seasickness. If you're going from Southampton around to the Med then it can be that it's a bit rough going down the side of France/Spain - but this can be easily overcome by getting a train down to Barcelona/Cadiz, South of France or Gerona and picking the boat up in the Med. I've done this on several occasions - we used to do it and get to the port a day or two early to have time in the port and make sure that we were there to embark on the the day. It's a lovely relaxed way to travel. Going to the Baltic is also lovely and when I went it was lovely and warm rather than stinking hot - so that might be a good compromise if you don't like heat.
I've also done centre parcs abroad - we went to a Dutch one, got the ferry over to calais, drove for about an hour, stayed in Ypres for the night and then went on to the parc (Het Heijdebos) another 3 hours drive away the next day, same thing in reverse on the way home. The Netherlands is a lovely country - some amazing beaches, lots of interesting places to explore (I spent many happy holidays there when I was in my tweens and teens too). And even taking into account the longer drive, the ferry and overnights in Ypres, it was still cheaper for us to go to a Dutch CP than a UK one... I haven't been to a uk one but the dutch ones didn't have lots of branded restaurants on site, it was all their own ones, good food if you wanted it and the one we went to had a huge second dome with a massive jungle exploration thing - think of a jungle themed soft play that's aimed at adults as well, it had caves, streams, rock climbing, rope bridges, zip wires, loads of jungle plants (even tropical birds flying around!), a bit like the jungle set on the Crystal maze if you remember that, that all the family enjoyed exploring.
If you do decide to go on French / european trains, then I think the booking opens 3 months before you travel or 2 months for Eurostar (or maybe it's the other way around) - talk to a travel agent and find out, as booking early will often net you the cheapest seats. We've used Railbookers who are a travel agency that specialise in rail travel - looking at their site would give you an idea of the prices and places easy to get to. Also look at the seat61.com website - written by an ex rail employee who loved travelling on Eurostar and exploring Europe (favourite seat was 61!) - it's been going well over 10 years and it's now a fabulous resource about how to travel by rail all over the world.
Having said all that I can see where your dh is coming from - for you, a holiday in the UK is fine because that's what you were used to and enjoyed so why do anything different. For him, if he had miserable times in the UK and/or was used to going to somewhere warm then it means that each year that you go somewhere in the UK you are reliving your happy childhood memory so to speak - while he doesn't ever get a turn.
In the name of fairness it probably is reasonable to let him choose somewhere other than the UK for a holiday every other year... Even if it is within the no fly and not too hot limitations. If you're in E Anglia could you get to Harwich easily and get a ferry over to Holland and then stay there or go further to Denmark, Finalnd, Estonia, etc. Could sea sickness bands and tablets help out if you know it's not going to be for too long? You'd end up in a lovely country with lots of places to explore and things to do with weather that's similar to ours but they usually seem to be just a smidge warmer and have better luck at staying nicer weather so your dh would get some warmth and you wouldn't be too hot...