Make your Bootstrap buttons big and fat on small touch devices, so they're easier to tap. Might help you to comply with ISO 9241-400:2007.

bootstrap-responsive-buttons.less

// conditionally make buttons block

@media (max-width: @screen-sm) {
    .btn-block-xs {
        .btn-block();
    }
}

@media (min-width: @screen-sm) and (max-width: @screen-md) {
    .btn-block-md {
        .btn-block();
    }
}

@media (min-width: @screen-md) and (max-width: @screen-lg) {
    .btn-block-lg {
        .btn-block();
    }
}

// conditionally make buttons big

@media (max-width: @screen-sm) {
    .btn-lg-xs {
        .btn-lg();
    }
}

@media (min-width: @screen-sm) and (max-width: @screen-md) {
    .btn-lg-md {
        .btn-lg();
    }
}

@media (min-width: @screen-md) and (max-width: @screen-lg) {
    .btn-lg-lg {
        .btn-lg();
    }
}

This is the above translated to SASS:

Add the following to bootstrap/_buttons.scss

.btn {
    @media (max-width: $screen-sm) {
        .btn-block-xs {
            @include btn-block();
        }
    }

    @media (min-width: $screen-sm) and (max-width: $screen-md) {
        .btn-block-md {
            @include btn-block();
        }
    }

    @media (min-width: $screen-md) and (max-width: $screen-lg) {
        .btn-block-lg {
            @include btn-block();
        }
    }

    // conditionally make buttons big

    @media (max-width: $screen-sm) {
        .btn-lg-xs {
            @include btn-lg();
        }
    }

    @media (min-width: $screen-sm) and (max-width: $screen-md) {
        .btn-lg-md {
            @include btn-lg();
        }
    }

    @media (min-width: $screen-md) and (max-width: $screen-lg) {
        .btn-lg-lg {
            @include btn-lg();
        }
    }
}

Add the following to bootstrap/mixins/_buttons.scss

@mixin btn_block()  {
    display: block;
    width: 100%;
}

@mixin btn-lg() {
    @include button-size($padding-large-vertical, $padding-large-horizontal, $font-size-large, $line-height-large, $border-radius-large);
}