I was in an almost identical position a few years ago and went with renting out the apartment. The apartment was modern and I'm into DIY, so maintenance was not an issue, and we had great tenants. But we sold it recently and I am delighted to be done with it.
We had a new baby (guess that could be on the horizon for you too) so getting a call at 8pm (early for most people, not if you've got a new born and are up all night!) that a pipe has started to leak, or tenants moving so you need to go vet new ones, attending AGMs and maybe being dragged onto the Board to do a stint, maybe discovering the building was not properly fire stopped and needs to be vacated or you need to pony up, messing around with another mortgage that you need to move/fix every now and then, collecting expenses and spending a couple of hours a year figuring them out with your accountant, considering the possible changes coming politically, damage, fire, theft, hold over tenants or bribing tenants to leave is all a lot of hassle for what, maybe (big maybe!) a percentage point or two over what you could earn just sticking it in the stock market completely passively?
I would not get back into it unless I was managing 10+ apartments so you could get some efficiencies and make a cushy job out of it. I think doing it otherwise is not a good choice, the risk:reward compared to other investments is just not worth it.
Get a bigger nicer PPR with the money and start paying down the mortgage aggressively and filling your pension.