This is where I would suggest you consult your local thesaurus...
But try the following:
Truth be told
indeed
truly
really
literally
as a matter of fact
in reality
or any of these that I got from a thesaurus (context dependent but words that might help you)...
adv. without a doubt
absolutely
actually
admittedly
as a matter of fact
assuredly
authentically
beyond doubt
categorically
certainly
de facto
easily
for real
genuinely
honestly
in actuality
in effect
in fact
in point of fact
in reality
indeed
indubitably
legitimately
literally
no ifs ands or buts
nothing else but
of course
positively
precisely
surely
truly
undoubtedly
unmistakably
unquestionably
verily
well
Nick