How far are you in building your product? Do it in Bubble (https://bubble.io/). Check it out and let me know what you think. I am not affiliated, just a fan.
‘Relativity’ would anyway be generic, non-descriptive for this product domain and cliche, but then to mispell it just to 'get a domain' (or whatever the logic was) seems poorly considered - every time I see 'relativty' it reads as a typo.