Unfair Dissmisal? HSE/Whistleblowing - would appreciate advice on next steps (England)

Earlier this month I was let go on the last week of my probation period. I understand that working with a business for less that two years means they do not need a reason for letting me go. However, I have a feeling the reasons they cited (difficult to work with/too corporate) could be to do with HSE and legal concerns that I had raised.

I'm now on garden leave and wondering what next steps to take, and if there is any recommended no upfront fee legal advice to take this further.

An overview of the issues I raised:

1. Water contamination (building was vacant for years prior to joining the business - was resolved after I escalted to wider team, I'veheaed they were aware of this prior to me joining)

2. No heating, they were looking to bring under 16 year olds into this space on a regular basis (Was resolved)

3. Lone working without risk assessments in place. (Not resolved)

4. Opening space to public without council permission, without public liability and adequate H&S plans including fire (not resolved).

I've spoken with ACAS but wanted to go forward with raising a grievance or taking further action.

Thanks