booster of the same vaccine form scientific point of view may be less effective than using different vaccines (when we are talking about vaccines with average same effect and type - i.e. both are 4th or 3rd generation)...

so, if you took Moderna, then next is better to be Pfizer, and opposite: if you took Pfizer then next is better to be Moderna... on this way your immunity will be boosted stronger, but side effects like 1-2 day high temperature may appear more often and will be stronger as well...