The monsters in Blood and Wine seem to be harder to fight than in the original game.
I, like most people, always have swallow and thunderbolt equipped.
The other two free slots I have white honey and Raffard's Decoction equipped.
Can anyone suggest a better option? I notice that Tawny Owl also seems to be a favorite for some.
Any suggestions to help me die less?

Depends on your build. Do you have any Alchemy skills for more toxicity? Tawny owl is great for using signs more quickly and goes well with Ekhidna decoction for health regen.

I don't make potions since I made ((Cat)) potion
others are useless (to me!)
cat is useful for everyone - at least more than torches!

Interesting. So doing quests in the dark with Tawny owl is the way to go? Maybe a bit of a problem seeing in the dark though.

I'd highly recommend finding the Superior Golden Oriole. There are several poison flinging enemies in Toussaint (Archespores, for one), and that potion makes poison heal you instead of damaging you. Makes battles against those enemies a cakewalk.

You would be surprised at just how light it is at night. I do pretty much all my roaming and quests at night and have never had to use cat except in the usual places, like caves.

The advantage gained at night with Sup Tawny Owl is incredible.

Pity, I have already completed Wine Wars - plenty Archespores I had problems with. Ekhidna decoction has 70% toxcity, very high and if I remove it with white honey does it not immediately remove all active potions?
I may be mistaken but prior to the ext. pack could you not consume a potion from your inventory without having to place it in a consumable slot as is the case now? (unless I am confusing this with Fallout 4.)

Decoctions work best with some Alchemy skils. For example, if you have acquired tolerance, tissue transformation, and hightened tolerance, you can run with two decoctions and 4 or 5 regular potions and get up to about 7500 health; well worth the 13 xp and 3 slots it takes. For 5 more xp use endure pain instead of Hightened torerance for up to 11K health.

I have recently completed Fallout 4 and just started Blood and Wine, having last played this game last year.
I am still getting back into it having forgotten a lot of the finer points. My skills tree have only blue and red items equipped
backed up with greater mutigens. Presumably the Alchemy skills you mention are a different color which would mean
even if I have them they are not equipped. Maybe I need to reset all my skill points and focus less on what the blue and red skills provide.

Yes, Alchemy skills are green. There certainly different ways to make a good character and you have to decide which is best for you. At the end, I always have 4 green slots: acquired Tolerance, tissue transformation, endure pain and synergy. Then one general slot (usually Griffin for the extra stamina ) and the remaining 7 slots either blue or red.

I see I have no alchemy skills. I now must decide whether to spend future skill points on this or keep two points for the "blood and wine" updated mutagen tree where 2 points are needed to unlock researched mutagens. (not yet sure how this works)
OR reset all my current skills.