MrsR8 Very difficult decision for you:
Look at the difference in the Euros you can buy for 1000 GBP and what you would obtain in GBP if you changed them right back again.
This is the transaction cost
This need to be considered when deciding - if you remain in the UK - whether to change to Euros
If you think you might emigrate, that is a very different matter
Pure currency speculation should only be done by those who know what they are doing and can afford to get back fewer pounds than they started with - because you will be buying groceries etc in Sterling.
imo a deal looks to have slightly more than 50:50 chance
However, that's still a big risk of no deal and if the deal is judged bad for trade, it could crash Sterling anyway 
On balance, if I weren't living in Germany, I wouldn't change more than I needed for any planned EU trip, but that's just me.
You might choose differently and find you were absolutely right
You could also compromise and convert a certain amount, to keep as Euro savings
Just try to separate your emotions - anger, loss and disgust over Brexit - from financial decisions and do what you think best.