Dear Sheetali,
Yours is a peculiar horoscope where in the 4th house 4 retrograde planets are placed.A natural benefic Jupitor is retro with natural malefics Rahu,Saturn and Mars all in retro. Jupitor is your 8th and 11th lord with exchange of house with Sun the 4th lord. You are in Guru Mahadasa till 8/2022.
I feel you have to pray/puja Lord shiva regularly to avoid such accidents , for long life and success.
In your case since Moon is exalted in lagna,you don't require a gemstone.
with best wishes,
USR