Notomato sauce.

A green pesto? Basil, olive oil, pine nuts and grated Parmesan with a dash of lemon.
Rocket or one of the spicy ‘Asian greens’ works too. Or spinach with a dash of chilli.

I’m not sure any of these would help with acid reflux, you need to cut out more than tomatoes

Yes, as ferry23 suggests, a white Bolognaise sauce with meat, onions, garlic, carrots, celery, white wine and a good stock would be an alternative. Known as Ragu Bianco.
You could add milk or cream according to some recipes. I wouldn't but that is a matter of preference.

How about using red peppers? You could roast them first with olive oil to bring out the flavour, then blitz them to make a purée.
I thinks I’d cook the mince and other ingredients first and then add the purée at the end, so not to spoil it’s flavour.

There’s a magic pill called Omazaprole, have you asked your GP?

Can’t you get your acid reflux sorted out?

Could you mix a small bit of tomato puree with stock and maybe add some chopped aubergine and/or mushrooms?

I can't really think of anything that truly replaces tomatoes in a spag bol.

You could try a white bolognese sauce - culinaryginger.com/traditional-white-bolognese-sauce/