Split up the chain of accesses into separate statements:

my $range = $worksheet -> UsedRange
    or die "No UsedRange found for $worksheet";
my $findresult = $range -> Find({What => "*", SearchDirection => xlPre
+vious, SearchOrder => xlByRows})
    or die "No result found for '*'";
my $row = $findresult -> {Row};
defined $row or die "No row found from $findresult";

my $col = $last_col = $findresult -> {Column};
defined $col or die "No col found from $findresult";
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This way, you don't have to climb down the chain to your search results twice even.

Also, I think I remember that a Range object in VBA has properties that give you the coordinates of the lower right cell directly. Maybe extract it from $range->{Address}...