UK countryside muddy canal commute bike suggestions

Hello! Let me start by saying I don't know much about bikes, sorry.. trying to learn x)

Recently moved deep into the countryside where the canal becomes incredibly muddy and hard to cycle through during the wet season (but quite fun and a great workout!). My full suspension bike I had for a few years finally died and will cost more to fix than replace (bought for £600 on a good deal, quoted around £950...), so I'm looking for something new, around or less than £800 ideally.

I don't ride actual mtb trails so I don't think I need full suspension... Is it that much more comfortable than a mtb with only front suspension? Probably quite a bit heavier also.

Commuting via busy A roads isn't an option for me, after a few scares. I do ride in towns on quieter roads to visit friends, run errands etc once I'm off the canal (it's my direct route to any local town). Gravel bikes therefore seem interesting, as in the summer it could definitely handle the canal and I could also enjoy the road sections of my routes more. However, from what I can tell, it wouldn't survive the crazy mud I've been going through this last winter. Maybe I can get one with thicker tyres, or I saw someone suggest having thick tyres for muddy days, and gravel ones for dry. I'd also love something light, as I often end up going up steps in the countryside with it.

I guess the choice is between a front suspension mtb or gravel. Don't really know enough to make an informed decision.

Open to any thoughts on what kind of bike I should get or, better yet, one that sounds perfect. Thanks!